U.S. patent application number 11/070390 was filed with the patent office on 2005-09-01 for method for selecting formulations to treat electrical cables.
This patent application is currently assigned to Novinium, Inc.. Invention is credited to Bertini, Glen John.
Application Number | 20050192708 11/070390 |
Document ID | / |
Family ID | 34919458 |
Filed Date | 2005-09-01 |
United States Patent
Application |
20050192708 |
Kind Code |
A1 |
Bertini, Glen John |
September 1, 2005 |
Method for selecting formulations to treat electrical cables
Abstract
A method for selecting components for a mixture to be injected
into an interstitial void volume adjacent to a central stranded
conductor of an electrical cable segment having the central
conductor encased in a polymeric insulation jacket to enhance the
dielectric properties of the cable segment. The method includes
selecting an anticipated operating temperature for the cable
segment to be used in selecting the components for the mixture to
be injected into the interstitial void volume of the cable segment
and selecting a minimum desired time period to be used in selecting
the compounds for the mixture to be injected during which the
dielectric properties of the cable segment are to be enhanced by
the mixture. Next, first, second and third components for the
mixture are selected to provide the cable segment with a reliable
life at the selected operating temperature spanning first, second
and third time periods, respectively.
Inventors: |
Bertini, Glen John; (Tacoma,
WA) |
Correspondence
Address: |
DAVIS WRIGHT TREMAINE, LLP
2600 CENTURY SQUARE
1501 FOURTH AVENUE
SEATTLE
WA
98101-1688
US
|
Assignee: |
Novinium, Inc.
Coupeville
WA
|
Family ID: |
34919458 |
Appl. No.: |
11/070390 |
Filed: |
March 1, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60549262 |
Mar 1, 2004 |
|
|
|
Current U.S.
Class: |
700/265 ;
264/262; 264/349; 700/98 |
Current CPC
Class: |
Y02A 30/14 20180101;
H01B 7/285 20130101 |
Class at
Publication: |
700/265 ;
264/262; 264/349; 700/098 |
International
Class: |
B29C 045/14; G06F
019/00 |
Claims
That which is claimed is:
1. A method for selecting components for a mixture to be injected
into an interstitial void volume adjacent to a central stranded
conductor of an electrical cable segment having the central
conductor encased in a polymeric insulation jacket to enhance the
dielectric properties of the cable segment, comprising: selecting
an anticipated operating temperature profile for the cable segment
to be used in selecting the components for the mixture to be
injected into the interstitial void volume of the cable segment;
selecting a minimum desired time period to be used in selecting the
compounds for the mixture to be injected into the interstitial void
volume of the cable segment during which the dielectric properties
of the cable segment are to be enhanced by the mixture; selecting a
first component for the mixture to provide the cable segment with a
reliable life spanning a first time period for the selected
operating temperature profile; selecting a second component for the
mixture to provide the cable segment with a reliable life spanning
a second time period at least in part extending beyond the first
time period for the selected operating temperature profile; and
selecting a third component for the mixture to provide the cable
segment with a reliable life spanning a third time period at least
in part extending beyond the second time period and beyond the
minimum desired time period for the selected operating temperature
profile.
2. A method for making a mixture to be injected into an
interstitial void volume adjacent to a central stranded conductor
of an electrical cable segment having the central conductor encased
in a polymeric insulation jacket to enhance the dielectric
properties of the cable segment, comprising: selecting an
anticipated operating temperature profile for the cable segment to
be used in selecting components for the mixture to be injected into
the interstitial void volume of the cable segment; selecting a
minimum desired time period to be used in selecting compounds for
the mixture to be injected into the interstitial void volume of the
cable segment during which the dielectric properties of the cable
segment are to be enhanced by the mixture; selecting a desired
quantity of the mixture to be injected into the interstitial void
volume of the cable segment to at least fill the interstitial void
volume adjacent to a central stranded conductor of the cable
segment; selecting first, second and third components for the
mixture in first, second and third quantities, respectively, to
produce at least the desired quantity of the mixture to be injected
into the interstitial void volume of the cable segment, with: the
first component for the mixture and the first quantity of the first
component to be included in the mixture being further selected so
as to provide the cable segment with a reliable life spanning a
first time period for the selected operating temperature profile,
the second component for the mixture and the second quantity of the
second component to be included in the mixture being further
selected so as to provide the cable segment with a reliable life
spanning a second time period at least in part extending beyond the
first time period for the selected operating temperature profile,
and the third component for the mixture and the third quantity of
the third component to be included in the mixture being further
selected so as to provide the cable segment with a reliable life
spanning a third time period at least in part extending beyond the
second time period and beyond the minimum desired time period for
the selected operating temperature profile; and mixing the first,
second and third quantities of the first, second and third
components together.
3. A method for making a mixture to be injected into an
interstitial void volume adjacent to a central stranded conductor
of an electrical cable segment having the central conductor encased
in a polymeric insulation jacket to enhance the dielectric
properties of the cable segment, comprising: selecting an
anticipated operating temperature profile for the cable segment to
be used in selecting components for the mixture to be injected into
the interstitial void volume of the cable segment; selecting a
minimum desired time period to be used in selecting compounds for
the mixture to be injected into the interstitial void volume of the
cable segment during which the dielectric properties of the cable
segment are to be enhanced by the mixture; selecting a desired
quantity of the mixture to be injected into the interstitial void
volume of the cable segment to at least fill the interstitial void
volume adjacent to a central stranded conductor of the cable
segment; selecting a first component for the mixture and a first
quantity of the first component to be included in the mixture to
produce a desired first concentration of the first component in the
mixture so as to provide the cable segment with a reliable life
spanning a first time period for the selected operating temperature
profile; selecting a second component for the mixture and a second
quantity of the second component to be included in the mixture to
produce a desired second concentration of the second component in
the mixture so as to provide the cable segment with a reliable life
spanning a second time period at least in part extending beyond the
first time period for the selected operating temperature profile;
selecting a third component for the mixture and a third quantity of
the third component to be included in the mixture to produce a
desired third concentration of the third component in the mixture
so as to provide the cable segment with a reliable life spanning a
third time period at least in part extending beyond the second time
period and beyond the minimum desired time period for the selected
operating temperature profile; and mixing the first, second and
third quantities of the first, second and third components
together.
4. A method for making a mixture to be injected into an
interstitial void volume adjacent to a central stranded conductor
of an electrical cable segment having the central conductor encased
in a polymeric insulation jacket to enhance the dielectric
properties of the cable segment, comprising: selecting an
anticipated operating temperature profile for the cable segment to
be used in selecting components for the mixture to be injected into
the interstitial void volume of the cable segment; selecting a
minimum desired time period to be used in selecting compounds for
the mixture to be injected into the interstitial void volume of the
cable segment during which the dielectric properties of the cable
segment are to be enhanced by the mixture; selecting a desired
quantity of the mixture to be injected into the interstitial void
volume of the cable segment to at least fill the interstitial void
volume adjacent to a central stranded conductor of the cable
segment; selecting a desired maximum price for the desired quantity
of the mixture to be injected into the interstitial void volume of
the cable segment; selecting first, second and third components for
the mixture in first, second and third quantities, respectively,
and having first, second and third prices, respectively, to produce
at least the desired quantity of the mixture to be injected into
the interstitial void volume of the cable segment with the first,
second and third prices of the first, second and third components
used to produce the desired quantity of the mixture having a
combined price no greater than the desired maximum price, with: the
first component for the mixture and the first quantity of the first
component to be included in the mixture being further selected so
as to provide the cable segment with a reliable life spanning a
first time period for the selected operating temperature profile,
the second component for the mixture and the second quantity of the
second component to be included in the mixture being further
selected so as to provide the cable segment with a reliable life
spanning a second time period at least in part extending beyond the
first time period for the selected operating temperature profile,
and the third component for the mixture and the third quantity of
the third component to be included in the mixture being further
selected so as to provide the cable segment with a reliable life
spanning a third time period at least in part extending beyond the
second time period and beyond the minimum desired time period for
the selected operating temperature profile; and mixing the first,
second and third quantities of the first, second and third
components together.
5. A method for enhancing the dielectric properties of an
electrical cable segment having a central stranded conductor
encased in a polymeric insulation jacket and having an interstitial
void volume in the region of the conductor, the method comprising:
selecting an anticipated operating temperature profile for the
cable segment to be used in selecting the components for a mixture
to be injected into the interstitial void volume of the cable
segment; selecting a minimum desired time period to be used in
selecting the compounds for the mixture to be injected into the
interstitial void volume of the cable segment during which the
dielectric properties of the cable segment are to be enhanced by
the mixture; selecting a first component for the mixture to provide
the cable segment with a reliable life spanning a first time period
for the selected operating temperature profile; selecting a second
component for the mixture to provide the cable segment with a
reliable life spanning a second time period at least in part
extending beyond the first time period for the selected operating
temperature profile; selecting a third component for the mixture to
provide the cable segment with a reliable life spanning a third
time period at least in part extending beyond the second time
period and beyond the minimum desired time period for the selected
operating temperature profile; injecting the mixture into the
interstitial void volume with the mixture at a pressure below the
elastic limit of the polymeric insulation jacket; and confining the
mixture within the interstitial void volume at a residual pressure
greater than about 50 psig, the pressure being imposed along the
entire length of the cable segment and being below the elastic
limit, whereby the residual pressure within the void volume
promotes the transport of the mixture into the polymeric insulation
jacket.
6. The method according to claim 5 for use with a cable segment
where the central stranded conductor is surrounded by a conductor
shield, wherein the mixture injected into the interstitial void
volume saturates the conductor shield and the polymeric insulation
jacket with the mixture, and wherein the mixture contained within
the interstitial void volume has a weight less than the weight of
the mixture required to saturate the conductor shield and the
polymeric insulation jacket.
7. The method according to claim 5, wherein the mixture is supplied
at a pressure greater than about 50 psig for more than about 2
hours before being confined within in the interstitial void
volume.
8. The method according to claim 5, wherein the pressure used in
injecting the interstitial void volume is greater than the residual
pressure.
9. The method according to claim 5, wherein the residual pressure
is about 100 psig to about 1000 psig.
10. The method according to claim 9, wherein the residual pressure
is about 300 psig to about 600 psig.
11. A method for enhancing the dielectric properties of an
electrical cable segment having a central stranded conductor
encased in a polymeric insulation jacket and having an interstitial
void volume in the region of the conductor, the cable segment
having a first closable high-pressure connector attached at one
terminus thereof and a second closable high-pressure connector
attached at another terminus thereof, each of the first and second
connectors providing fluid communication to the interstitial void
volume, the method comprising: selecting an anticipated operating
temperature profile for the cable segment to be used in selecting
the components for a mixture to be injected into the interstitial
void volume of the cable segment; selecting a minimum desired time
period to be used in selecting the compounds for the mixture to be
injected into the interstitial void volume of the cable segment
during which the dielectric properties of the cable segment are to
be enhanced by the mixture; selecting a first component for the
mixture to provide the cable segment with a reliable life spanning
a first time period for the selected operating temperature profile;
selecting a second component for the mixture to provide the cable
segment with a reliable life spanning a second time period at least
in part extending beyond the first time period for the selected
operating temperature profile; selecting a third component for the
mixture to provide the cable segment with a reliable life spanning
a third time period at least in part extending beyond the second
time period and beyond the minimum desired time period for the
selected operating temperature profile; opening both the first and
second connectors and introducing the mixture via the first
connector so as to fill the interstitial void volume; closing the
second connector and introducing an additional quantity of the
mixture via the first connector at a pressure greater than about 50
psig, but less than the elastic limit of the polymeric insulation
jacket; and closing the first connector so as to contain the
mixture within the interstitial void volume at a residual pressure
greater than about 50 psig, but below the elastic limit, whereby
the pressure within the interstitial void volume promotes the
transport of the mixture into the polymeric insulation jacket.
12. A method for enhancing the dielectric properties of an
electrical cable segment between first and second connectors, the
cable segment having a central stranded conductor encased in a
polymeric insulation jacket and having an interstitial void volume
in the region of the conductor, the method comprising: selecting an
anticipated operating temperature profile for the cable segment to
be used in selecting the components for a mixture to be injected
into the interstitial void volume of the cable segment; selecting a
minimum desired time period to be used in selecting the compounds
for the mixture to be injected into the interstitial void volume of
the cable segment during which the dielectric properties of the
cable segment are to be enhanced by the mixture; selecting a first
component for the mixture to provide the cable segment with a
reliable life spanning a first time period for the selected
operating temperature profile; selecting a second component for the
mixture to provide the cable segment with a reliable life spanning
a second time period at least in part extending beyond the first
time period for the selected operating temperature profile;
selecting a third component for the mixture to provide the cable
segment with a reliable life spanning a third time period at least
in part extending beyond the second time period and beyond the
minimum desired time period for the selected operating temperature
profile; filling through at least one of the first and second
connectors the interstitial void volume along the entire length of
the cable segment with the mixture at a pressure below the elastic
limit of the polymeric insulation jacket; and confining with the
first and second connectors the mixture within the interstitial
void volume at a residual pressure selected to promote the
transport of the mixture into the polymeric insulation jacket, with
the residual pressure being imposed along the entire length of the
cable segment and being below the elastic limit.
13. The method according to claim 12, wherein the residual pressure
at which the mixture is confined within the interstitial void
volume is sufficient to expand the interstitial void volume along
the entire length of the cable segment by at least 5%, but below an
elastic limit of the polymeric insulation jacket.
14. The method according to claim 12, wherein the filling and
confining of the mixture within the interstitial void volume
includes: attaching the first connector to a first terminus of the
cable segment; attaching the second connector to a second terminus
of the cable segment, each of the first and second connectors
providing fluid communication to the interstitial void volume;
opening both of the first and second connectors and introducing the
mixture via the first connector so as to fill the interstitial void
volume; closing the second connector and introducing an additional
quantity of the mixture via the first connector at a pressure
greater than about 50 psig, but less than an elastic limit of the
polymeric insulation jacket; and closing the first connector so as
to contain the mixture within the interstitial void volume at a
residual pressure greater than about 50 psig, but below the elastic
limit.
15. A method for selecting a mixture to be injected into an
interstitial void volume adjacent to a central stranded conductor
of an electrical cable segment having the central conductor encased
in a polymeric insulation jacket to enhance the dielectric
properties of the cable segment, comprising: selecting an
anticipated operating temperature profile for the cable segment to
be used in selecting components for the mixture to be injected into
the interstitial void volume of the cable segment; selecting a
minimum desired time period to be used in selecting compounds for
the mixture to be injected into the interstitial void volume of the
cable segment during which the dielectric properties of the cable
segment are to be enhanced by the mixture; selecting a desired
quantity of the mixture to be injected into the interstitial void
volume of the cable segment to at least fill the interstitial void
volume adjacent to a central stranded conductor of the cable
segment; and selecting first, second and third components for the
mixture in first, second and third quantities, respectively, to
produce at least the desired quantity of the mixture to be injected
into the interstitial void volume of the cable segment, with: the
first component for the mixture and the first quantity of the first
component to be included in the mixture being further selected so
as to provide the cable segment with a reliable life spanning a
first time period for the selected operating temperature profile,
the second component for the mixture and the second quantity of the
second component to be included in the mixture being further
selected so as to provide the cable segment with a reliable life
spanning a second time period at least in part extending beyond the
first time period for the selected operating temperature profile,
and the third component for the mixture and the third quantity of
the third component to be included in the mixture being further
selected so as to provide the cable segment with a reliable life
spanning a third time period at least in part extending beyond the
second time period and beyond the minimum desired time period for
the selected operating temperature profile.
16. A method for selecting a mixture to be injected into an
interstitial void volume adjacent to a central stranded conductor
of an electrical cable segment having the central conductor encased
in a polymeric insulation jacket to enhance the dielectric
properties of the cable segment, comprising: selecting an
anticipated operating temperature profile for the cable segment to
be used in selecting components for the mixture to be injected into
the interstitial void volume of the cable segment; selecting a
minimum desired time period to be used in selecting compounds for
the mixture to be injected into the interstitial void volume of the
cable segment during which the dielectric properties of the cable
segment are to be enhanced by the mixture; selecting a desired
quantity of the mixture to be injected into the interstitial void
volume of the cable segment to at least fill the interstitial void
volume adjacent to a central stranded conductor of the cable
segment; selecting a first component for the mixture and a first
quantity of the first component to be included in the mixture to
produce a desired first concentration of the first component in the
mixture so as to provide the cable segment with a reliable life
spanning a first time period for the selected operating temperature
profile; selecting a second component for the mixture and a second
quantity of the second component to be included in the mixture to
produce a desired second concentration of the second component in
the mixture so as to provide the cable segment with a reliable life
spanning a second time period at least in part extending beyond the
first time period for the selected operating temperature profile;
and selecting a third component for the mixture and a third
quantity of the third component to be included in the mixture to
produce a desired third concentration of the third component in the
mixture so as to provide the cable segment with a reliable life
spanning a third time period at least in part extending beyond the
second time period and beyond the minimum desired time period for
the selected operating temperature profile.
17. A method for selecting a mixture to be injected into an
interstitial void volume adjacent to a central stranded conductor
of an electrical cable segment having the central conductor encased
in a polymeric insulation jacket to enhance the dielectric
properties of the cable segment, comprising: selecting an
anticipated operating temperature profile for the cable segment to
be used in selecting components for the mixture to be injected into
the interstitial void volume of the cable segment; selecting a
minimum desired time period to be used in selecting compounds for
the mixture to be injected into the interstitial void volume of the
cable segment during which the dielectric properties of the cable
segment are to be enhanced by the mixture; selecting a desired
quantity of the mixture to be injected into the interstitial void
volume of the cable segment to at least fill the interstitial void
volume adjacent to a central stranded conductor of the cable
segment; selecting a desired maximum price for the desired quantity
of the mixture to be injected into the interstitial void volume of
the cable segment; and selecting first, second and third components
for the mixture in first, second and third quantities,
respectively, and having first, second and third prices,
respectively, to produce at least the desired quantity of the
mixture to be injected into the interstitial void volume of the
cable segment with the first, second and third prices of the first,
second and third components used to produce the desired quantity of
the mixture having a combined price no greater than the desired
maximum price, with: the first component for the mixture and the
first quantity of the first component to be included in the mixture
being further selected so as to provide the cable segment with a
reliable life spanning a first time period for the selected
operating temperature profile, the second component for the mixture
and the second quantity of the second component to be included in
the mixture being further selected so as to provide the cable
segment with a reliable life spanning a second time period at least
in part extending beyond the first time period for the selected
operating temperature profile, and the third component for the
mixture and the third quantity of the third component to be
included in the mixture being further selected so as to provide the
cable segment with a reliable life spanning a third time period at
least in part extending beyond the second time period and beyond
the minimum desired time period for the selected operating
temperature profile.
18. A method for selecting at least one dielectric
property-enhancing fluid to be injected into an interstitial void
volume adjacent to a central stranded conductor of an electrical
cable segment having the central conductor encased in a polymeric
insulation jacket to enhance the dielectric properties of the cable
segment, comprising: selecting an anticipated operating temperature
profile for the cable segment to be used in selecting the at least
one dielectric property-enhancing fluid to be injected into the
interstitial void volume of the cable segment; selecting a minimum
desired time period to be used in selecting the at least one
dielectric property-enhancing fluid to be injected into the
interstitial void volume of the cable segment during which the
dielectric properties of the cable segment are to be enhanced by
the at least one dielectric property-enhancing fluid; selecting the
at least one dielectric property-enhancing fluid to provide the
cable segment with a reliable life spanning at least the minimum
desired time period for the selected operating temperature
profile.
19. The method according to claim 18, wherein selecting the at
least one dielectric property-enhancing fluid includes selecting at
least first and second components for a mixture to be injected into
the interstitial void volume of the cable segment, with the first
component for the mixture to provide the cable segment with a
reliable life spanning a first time period for the selected
operating temperature profile, and the second component for the
mixture to provide the cable segment with a reliable life spanning
a second time period at least in part extending beyond the first
time period for the selected operating temperature profile.
20. The method according to claim 19, wherein selecting the at
least one dielectric property-enhancing fluid further includes
selecting a third component for the mixture to be injected into the
interstitial void volume of the cable segment, with the third
component for the mixture to provide the cable segment with a
reliable life spanning a third time period at least in part
extending beyond the second time period and beyond the minimum
desired time period for the selected operating temperature profile
and with the third component being a combination of at least two
constituent components, each to provide the cable segment with a
reliable life spanning at least a portion of the third time period
for the selected operating temperature profile.
21. The method according to claim 18, wherein the selected
operating temperature profile is selected at least in part based on
the anticipated fluctuations over time of the difference between
the anticipated operating temperature of the central conductor and
the anticipated temperature of an outer portion of the polymeric
insulation jacket during operation of the central conductor during
at least a portion of the minimum desired time period.
22. A method for selecting a mixture to be injected into an
interstitial void volume adjacent to a central stranded conductor
of an electrical cable segment having the central conductor encased
in a polymeric insulation jacket to enhance the dielectric
properties of the cable segment, comprising: selecting an
anticipated operating temperature profile for the cable segment to
be used in selecting components for the mixture to be injected into
the interstitial void volume of the cable segment; selecting a
minimum desired time period to be used in selecting compounds for
the mixture to be injected into the interstitial void volume of the
cable segment during which the dielectric properties of the cable
segment are to be enhanced by the mixture; selecting a desired
quantity of the mixture to be injected into the interstitial void
volume of the cable segment; and selecting at least first and
second components for the mixture in first and second quantities,
respectively, to produce at least the desired quantity of the
mixture to be injected into the interstitial void volume of the
cable segment, with: the first component for the mixture and the
first quantity of the first component to be included in the mixture
being further selected so as to provide the cable segment with a
reliable life spanning a first time period for the selected
operating temperature profile, and the second component for the
mixture and the second quantity of the second component to be
included in the mixture being further selected so as to provide the
cable segment with a reliable life spanning a second time period at
least in part extending beyond the first time period for the
selected operating temperature profile.
23. A method for selecting a mixture to be injected into an
interstitial void volume adjacent to a central stranded conductor
of an electrical cable segment having the central conductor encased
in a polymeric insulation jacket to enhance the dielectric
properties of the cable segment, comprising: selecting an
anticipated operating temperature profile for the cable segment to
be used in selecting components for the mixture to be injected into
the interstitial void volume of the cable segment; selecting a
minimum desired time period to be used in selecting compounds for
the mixture to be injected into the interstitial void volume of the
cable segment during which the dielectric properties of the cable
segment are to be enhanced by the mixture; selecting a desired
quantity of the mixture to be injected into the interstitial void
volume of the cable segment; selecting a first component for the
mixture and a first quantity of the first component to be included
in the mixture to produce a desired first concentration of the
first component in the mixture so as to provide the cable segment
with a reliable life spanning a first time period for the selected
operating temperature profile; and selecting a second component for
the mixture and a second quantity of the second component to be
included in the mixture to produce a desired second concentration
of the second component in the mixture so as to provide the cable
segment with a reliable life spanning a second time period at least
in part extending beyond the first time period for the selected
operating temperature profile.
24. A method for selecting a mixture to be injected into an
interstitial void volume adjacent to a central stranded conductor
of an electrical cable segment having the central conductor encased
in a polymeric insulation jacket to enhance the dielectric
properties of the cable segment, comprising: selecting an
anticipated operating temperature profile for the cable segment to
be used in selecting components for the mixture to be injected into
the interstitial void volume of the cable segment; selecting a
minimum desired time period to be used in selecting compounds for
the mixture to be injected into the interstitial void volume of the
cable segment during which the dielectric properties of the cable
segment are to be enhanced by the mixture; selecting a desired
quantity of the mixture to be injected into the interstitial void
volume of the cable segment; selecting a desired maximum price for
the desired quantity of the mixture to be injected into the
interstitial void volume of the cable segment; and selecting at
least first and second components for the mixture in first and
second quantities, respectively, and having first and second
prices, respectively, to produce at least the desired quantity of
the mixture to be injected into the interstitial void volume of the
cable segment with the first and second prices of the first and
second components used to produce the desired quantity of the
mixture having a combined price no greater than the desired maximum
price, with: the first component for the mixture and the first
quantity of the first component to be included in the mixture being
further selected so as to provide the cable segment with a reliable
life spanning a first time period for the selected operating
temperature profile, and the second component for the mixture and
the second quantity of the second component to be included in the
mixture being further selected so as to provide the cable segment
with a reliable life spanning a second time period at least in part
extending beyond the first time period for the selected operating
temperature profile.
25. A method for enhancing the dielectric properties of an
electrical cable segment having a central stranded conductor
encased in a polymeric insulation jacket and having an interstitial
void volume in the region of the conductor, the method comprising:
selecting an anticipated operating temperature profile for the
cable segment to be used in selecting at least one dielectric
property-enhancing fluid to be injected into the interstitial void
volume of the cable segment; selecting a minimum desired time
period to be used in selecting the at least one dielectric
property-enhancing fluid to be injected into the interstitial void
volume of the cable segment during which the dielectric properties
of the cable segment are to be enhanced by the mixture; selecting
the at least one dielectric property-enhancing fluid to provide the
cable segment with a reliable life spanning at least the minimum
desired time period for the selected operating temperature profile;
injecting the at least one dielectric property-enhancing fluid into
the interstitial void volume with the at least one dielectric
property-enhancing fluid at a pressure below the elastic limit of
the polymeric insulation jacket; and confining the at least one
dielectric property-enhancing fluid within the interstitial void
volume at a residual pressure greater than about 50 psig, the
pressure being imposed along the entire length of the cable segment
and being below the elastic limit, whereby the residual pressure
within the interstitial void volume promotes the transport of the
at least one dielectric property-enhancing fluid into the polymeric
insulation jacket.
26. The method according to claim 25, wherein selecting the at
least one dielectric property-enhancing fluid includes selecting at
least first and second components for a mixture to be injected into
the interstitial void volume of the cable segment, with the first
component for the mixture to provide the cable segment with a
reliable life spanning a first time period for the selected
operating temperature profile, and the second component for the
mixture to provide the cable segment with a reliable life spanning
a second time period at least in part extending beyond the first
time period for the selected operating temperature profile.
27. The method according to claim 26, wherein selecting the at
least one dielectric property-enhancing fluid further includes
selecting a third component for the mixture to be injected into the
interstitial void volume of the cable segment, with the third
component for the mixture to provide the cable segment with a
reliable life spanning a third time period at least in part
extending beyond the second time period and beyond the minimum
desired time period for the selected operating temperature profile
and with the third component being a combination of at least two
constituent components, each to provide the cable segment with a
reliable life spanning at least a portion of the third time period
for the selected operating temperature profile.
28. The method according to claim 25, wherein the selected
operating temperature profile is selected at least in part based on
the anticipated fluctuations over time of the difference between
the anticipated operating temperature of the central conductor and
the anticipated temperature of an outer portion of the polymeric
insulation jacket during operation of the central conductor during
at least a portion of the minimum desired time period.
29. The method according to claim 25 for use with a cable segment
where the central stranded conductor is surrounded by a conductor
shield, wherein the at least one dielectric property-enhancing
fluid injected into the interstitial void volume saturates the
conductor shield and the polymeric insulation jacket with the at
least one dielectric property-enhancing fluid, and wherein the at
least one dielectric property-enhancing fluid contained within the
interstitial void volume has a weight less than the weight of the
at least one dielectric property-enhancing fluid required to
saturate the conductor shield and the polymeric insulation
jacket.
30. The method according to claim 25, wherein the at least one
dielectric property-enhancing fluid is supplied at a pressure
greater than about 50 psig for more than about 2 hours before being
confined within in the interstitial void volume.
31. The method according to claim 25, wherein the pressure used in
injecting the interstitial void volume is greater than the residual
pressure.
32. The method according to claim 25, wherein the residual pressure
is about 100 psig to about 1000 psig.
33. The method according to claim 32, wherein the residual pressure
is about 300 psig to about 600 psig.
34. A method for enhancing the dielectric properties of an
electrical cable segment between first and second connectors, the
cable segment having a central stranded conductor encased in a
polymeric insulation jacket and having an interstitial void volume
in the region of the conductor, the method comprising: selecting an
anticipated operating temperature profile for the cable segment to
be used in selecting at least one dielectric property-enhancing
fluid to be injected into the interstitial void volume of the cable
segment; selecting a minimum desired time period to be used in
selecting the at least one dielectric property-enhancing fluid to
be injected into the interstitial void volume of the cable segment
during which the dielectric properties of the cable segment are to
be enhanced by the mixture; selecting the at least one dielectric
property-enhancing fluid to provide the cable segment with a
reliable life spanning at least the minimum desired time period for
the selected operating temperature profile; filling through at
least one of the first and second connectors the interstitial void
volume along the entire length of the cable segment with the at
least one dielectric property-enhancing fluid at a pressure below
the elastic limit of the polymeric insulation jacket; and confining
with the first and second connectors the at least one dielectric
property-enhancing fluid within the interstitial void volume at a
residual pressure selected to promote the transport of the at least
one dielectric property-enhancing fluid into the polymeric
insulation jacket, with the residual pressure being imposed along
the entire length of the cable segment and being below the elastic
limit.
35. The method according to claim 34, wherein the residual pressure
at which the at least one dielectric property-enhancing fluid is
confined within the interstitial void volume is sufficient to
expand the interstitial void volume along the entire length of the
cable segment by at least 5%, but below an elastic limit of the
polymeric insulation jacket.
36. The method according to claim 34, wherein the filling and
confining of the at least one dielectric property-enhancing fluid
within the interstitial void volume includes: attaching the first
connector to a first terminus of the cable segment; attaching the
second connector to a second terminus of the cable segment, each of
the first and second connectors providing fluid communication to
the interstitial void volume; opening both of the first and second
connectors and introducing the at least one dielectric
property-enhancing fluid via the first connector so as to fill the
interstitial void volume; closing the second connector and
introducing an additional quantity of the at least one dielectric
property-enhancing fluid via the first connector at a pressure
greater than about 50 psig, but less than an elastic limit of the
polymeric insulation jacket; and closing the first connector so as
to contain the at least one dielectric property-enhancing fluid
within the interstitial void volume at a residual pressure greater
than about 50 psig, but below the elastic limit.
37. The method according to claim 34, wherein selecting the at
least one dielectric property-enhancing fluid includes selecting at
least first and second components for a mixture to be injected into
the interstitial void volume of the cable segment, with the first
component for the mixture to provide the cable segment with a
reliable life spanning a first time period for the selected
operating temperature profile, and the second component for the
mixture to provide the cable segment with a reliable life spanning
a second time period at least in part extending beyond the first
time period for the selected operating temperature profile.
38. The method according to claim 34, wherein selecting the at
least one dielectric property-enhancing fluid further includes
selecting a third component for the mixture to be injected into the
interstitial void volume of the cable segment, with the third
component for the mixture to provide the cable segment with a
reliable life spanning a third time period at least in part
extending beyond the second time period and beyond the minimum
desired time period for the selected operating temperature profile
and with the third component being a combination of at least two
constituent components, each to provide the cable segment with a
reliable life spanning at least a portion of the third time period
for the selected operating temperature profile.
39. The method according to claim 34, wherein the selected
operating temperature profile is selected at least in part based on
the anticipated fluctuations over time of the difference between
the anticipated operating temperature of the central conductor and
the anticipated temperature of an outer portion of the polymeric
insulation jacket during operation of the central conductor during
at least a portion of the minimum desired time period.
40. The method according to claim 34 for use with a cable segment
where the central stranded conductor is surrounded by a conductor
shield, wherein the at least one dielectric property-enhancing
fluid filling the interstitial void volume saturates the conductor
shield and the polymeric insulation jacket with the at least one
dielectric property-enhancing fluid, and wherein the at least one
dielectric property-enhancing fluid contained within the
interstitial void volume has a weight less than the weight of the
at least one dielectric property-enhancing fluid required to
saturate the conductor shield and the polymeric insulation
jacket.
41. The method according to claim 34, wherein the at least one
dielectric property-enhancing fluid is supplied at a pressure
greater than about 50 psig for more than about 2 hours before being
confined within in the interstitial void volume.
42. The method according to claim 34, wherein the pressure used in
filling the interstitial void volume is greater than the residual
pressure.
43. The method according to claim 34, wherein the residual pressure
is about 100 psig to about 1000 psig.
44. The method according to claim 43, wherein the residual pressure
is about 300 psig to about 600 psig.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for enhancing the
dielectric strength of an electrical power cable and, more
particularly, relates to an efficient and effective method for
selecting formulations to treat electrical cable segments.
[0003] 2. Description of the Related Art
[0004] Extensive networks of underground electrical cables are in
place in many parts of the industrialized world. Such underground
distribution offers great advantage over conventional overhead
lines in that it is not subject to wind, ice or lightning damage
and is thus viewed as a reliable means for delivering electrical
power without obstructing the surrounding landscape, the latter
feature being particularly appreciated in suburban and urban
settings. Unfortunately, these cables, which generally comprise a
stranded conductor surrounded by a semi-conducting shield, a layer
of insulation jacket, and an insulation shield, often suffer
premature breakdown and do not attain their originally anticipated
longevity of 30 to 40 years. Their dielectric breakdown is
generally attributed to at least two so-called "treeing" phenomena
which lead to a progressive degradation of the cable's insulation.
The first, "electrical treeing," is the product of numerous
electrical discharges in the presence of strong electrical fields
which eventually lead to the formation of microscopic branching
channels within the insulation material, from which the descriptive
terminology derives. A similar mechanism, "water treeing," is
observed when the insulation material is simultaneously exposed to
moisture and an electric field. Although the latter mechanism is
much more gradual than electrical treeing, it does occur at
considerably lower electrical fields and therefore is considered to
be a primary contributor to reduced cable service life. Since
replacing a failed section of underground cable can be a very
costly and involved procedure, there is a strong motivation on the
part of the electrical utility industry to extend the useful life
of existing underground cables in a cost-effective manner.
[0005] Two early efforts by Bahder and Fryszczyn focused on
rejuvenating in-service cables by either simply drying the
insulation or introducing a certain liquid into the void volume
associated with the conductor geometry after such a drying step.
Thus, in U.S. Pat. No. 4,545,133 the inventors teach a method for
retarding electrochemical decomposition of a cable's insulation by
continuously passing a dry gas through the interior of the cable.
Only nitrogen is explicitly recited as the gas to be used and
maximum pressure contemplated for introducing the gas is 50 psig
(pounds per square inch above atmospheric pressure). Not only is
this method cumbersome, but it requires extensive monitoring and
scheduled replenishment of the dry gas supply. U.S. Pat. No.
4,372,988 to Bahder teaches a method for reclaiming electrical
distribution cable which comprises drying the cable and then
continuously supplying a tree retardant liquid to the interior of
the cable. The liquid was believed to diffuse out of the cable's
interior and into the insulation, where it filled the microscopic
trees and thereby augmented the service life of the cable. This
disclosure suffers from the disadvantage that the retardant can
exude or leak from the cable. The loss of liquid was addressed by a
preferred embodiment wherein external reservoirs suitable for
maintaining a constant level of the liquid were provided, further
adding to the complexity of this method.
[0006] An improvement over the disclosure by Bahder was proposed by
Vincent et al. in U.S. Pat. No. 4,766,011, wherein the tree
retardant liquid was selected from a particular class of aromatic
alkoxysilanes. Again, the tree retardant was supplied to the
interstices of the cable conductor. However, in this case, the
fluid can polymerize within the cable's interior as well as within
the water tree voids in the insulation and therefore does not leak
out of the cable, or only exudes therefrom at a low rate. This
method and variations thereof employing certain rapidly diffusing
components (see U.S. Pat. Nos. 5,372,840 and 5,372,841) have
enjoyed commercial success over the last decade or so, but they
still have some practical limitations when reclaiming underground
residential distribution (URD) cables, which have a relatively
small diameter, and therefore present insufficient interstitial
volume relative to the amount of retardant required for optimum
dielectric performance. Thus, although not explicitly required by
the above mentioned disclosures, a typical in-the-field reclamation
of URD cables employing such silane-based compositions typically
leaves a liquid reservoir connected to the cable for a 60 to 90 day
"soak period" to allow sufficient retardant liquid to penetrate the
cable insulation and thereby restore the dielectric properties. For
example, cables having round conductors smaller than 4/0 (120
mm.sup.2) generally require the above described reservoir and soak
period to introduce a sufficient amount of treating fluid. In
reality, this is an oversimplification, since some cables larger
than 4/0 with compressed or compacted strands would suffer from the
same inadequate fluid supply. As a result, it is generally
necessary to have a crew visit the site at least three times: first
to begin the injection which involves a vacuum at one end and a
slightly pressurized feed reservoir on the other end, second to
remove the vacuum bottle a few days later after the fluid has
traversed the length of the cable segment, and finally to remove
the reservoir after the soak period is complete. The repetitive
trips are costly in terms of human resource. Moreover, each
exposure of workers to energized equipment presents additional risk
of serious injury or fatality and it would be beneficial to
minimize such interactions. In view of the above limitations, a
circuit owner might find it economically equivalent, or even
advantageous, to completely replace a cable once it has
deteriorated rather than resort to the above restorative
methods.
[0007] Unlike the above described URD systems, large diameter
(e.g., feeder) cables present their own unique problems. Because of
the relatively larger interstitial volumes of the latter, the
amount of retardant liquid introduced according to the above
described methods can actually exceed that required to optimally
treat the insulation. Such systems do not require the above
described reservoir, but, as the temperature of the treated cable
cycles with electrical load, thermodynamic pumping of ever more
liquid from the cable's core into the insulation was believed to be
responsible for the catastrophic bursting of some cables. This
"supersaturation" phenomenon, and a remedy therefor, are described
in U.S. Pat. No. 6,162,491 to Bertini. In this variation of the
above described methods, a diluent, which has a low viscosity, is
insoluble in the insulation and is miscible with the retardant
liquid, is added to the latter, thereby limiting the amount of
retardant which can diffuse into the insulation. A methodology for
determining the proper amount of the diluent for a given situation
is provided. While this method may indeed prevent the bursting of
large cables after treatment it does not take advantage of the
extra interstitial volume by employing a diluent which is incapable
of providing any benefit to the long-term dielectric performance of
the insulation. Thus, this method does not take advantage of the
large interstitial volume associated with such cables.
[0008] In all of the above recited methods for treating in-service
cables, the retardant liquid is injected into the cable under a
pressure sufficient to facilitate filling the interstitial void
volume. But, although pressures as high as 400 psig have been
employed to this end (e.g., Transmission & Distribution World,
Jul. 1, 1999, "Submarine Cable Rescued With Silicone-Based Fluid"),
the pressure is always discontinued after the cable is filled. At
most, a residual pressure of up to 30 psig is applied to a liquid
reservoir after injection, as required for the soak period in the
case of URD cable reclamation. And, while relatively high pressures
have been used to inject power cables, this prior use is solely to
accelerate the cable segment filling time, especially for very long
lengths as are encountered with submarine cables (the above
Transmission & Distribution World article), and the pressure
was relieved after the cable segment was filled. Furthermore, even
when higher pressures were maintained in an experimental
determination of possible detrimental effects of excessive
pressure, the pressure was maintained for only a brief period by an
external pressure reservoir to simulate the injection of longer
segment lengths than those employed in the experiment ("Entergy
Metro Case Study: Post-Treatment Lessons," Glen Bertini, ICC April,
1997 Meeting, Scottsdale, Ariz.). In this case, even after two
hours of continuous pressure at 117 psig, the interstitial void
volume of the cable segment was not completely filled and it was
suggested that the inability to completely fill the interstices was
due to severe strand compaction.
[0009] While injection to extend the life of power cables has been
in wide-spread use for two decades, in each case a single active
formulation (either an essentially pure compound or a mixture) is
pumped into cables to extend life (see U.S. Pat. Nos. 4,372,988;
4,766,011; 5,372,840 and 5,372,841). While each of these prior art
patents suggests that mixtures of materials might be efficacious,
they do not suggest a method to optimize the total quantity and
total concentration of each component in a mixture to match the
unique geometry, condition, and anticipated operation of each
cable. In some cases, where there are larger conductors with less
severe compaction, there may be more interstitial volume available
within the strand interstices than required to treat the cable. The
prior art approach does disclose the addition of non-active
dilutants to mitigate potential conditions of super saturation (see
U.S. Pat. No. 6,162,491). But, in each and every case a single
formulation of active ingredients is utilized.
BRIEF SUMMARY OF THE INVENTION
[0010] A method for selecting components for a mixture to be
injected into an interstitial void volume adjacent to a central
stranded conductor of an electrical cable segment having the
central conductor encased in a polymeric insulation jacket to
enhance the dielectric properties of the cable segment. The method
includes selecting an anticipated operating temperature for the
cable segment to be used in selecting the components for the
mixture to be injected into the interstitial void volume of the
cable segment; and selecting a minimum desired time period to be
used in selecting the compounds for the mixture to be injected into
the interstitial void volume of the cable segment during which the
dielectric properties of the cable segment are to be enhanced by
the mixture. Next, the method includes selecting a first component
for the mixture to provide the cable segment with a reliable life
at the selected operating temperature spanning a first time period;
selecting a second component for the mixture to provide the cable
segment with a reliable life at the selected operating temperature
spanning a second time period at least in part extending beyond the
first time period; and selecting a third component for the mixture
to provide the cable segment with a reliable life at the selected
operating temperature spanning a third time period at least in part
extending beyond the second time period and beyond the minimum
desired time period. In another aspect, a method is provided for
making a mixture to be injected into the interstitial void volume
of the cable segment including selecting the anticipated operating
temperature and the minimum desired time period as noted above, and
also selecting a desired quantity of the mixture to be injected
into the interstitial void volume of the cable segment to at least
fill the interstitial void volume, selecting first, second and
third components for the mixture in first, second and third
quantities, respectively, to produce at least the desired quantity
of the mixture to be injected into the interstitial void volume,
with: the first component for the mixture and the first quantity of
the first component to be included in the mixture being further
selected so as to provide the cable segment with a reliable life at
the selected operating temperature spanning a first time period,
the second component for the mixture and the second quantity of the
second component to be included in the mixture being further
selected so as to provide the cable segment with a reliable life at
the selected operating temperature spanning a second time period at
least in part extending beyond the first time period, and the third
component for the mixture and the third quantity of the third
component to be included in the mixture being further selected so
as to provide the cable segment with a reliable life at the
selected operating temperature spanning a third time period at
least in part extending beyond the second time period and beyond
the minimum desired time period. The method further including
mixing the first, second and third quantities of the first, second
and third components together.
[0011] Other features and advantages of the invention will become
apparent from the following detailed description, taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0012] FIG. 1 is a plot of actual measured weight (top curve), and
calculated weight (bottom curve), of acetophenone injected into a
cable segment as a function of injection pressure, the respective
weights being normalized to a 1000 foot cable length.
[0013] FIG. 2 is a plot of the pressure decay observed as a
function of time after the cable segment of FIG. 1 was filled and
the acetophenone confined under the indicated pressures.
[0014] FIG. 3 is a cross-sectional view of a high-pressure terminal
connector used to inject acetophenone into the cable segment of
FIG. 1.
[0015] FIG. 3A is plan view of the washer of FIG. 3 and associated
set-screws.
[0016] FIG. 4 is a perspective view of the assembled connector of
FIG. 3 showing use of a split ring collar.
[0017] FIG. 5 is a partial cross-sectional view of a swagable
high-pressure, integral housing terminal connector having machined
teeth in the swaging regions.
[0018] FIG. 6 is an enlarged, cross-sectional view of the
self-closing spring-actuated injection valve of FIG. 5 showing an
associated injection needle used to supply fluid to the
high-pressure terminal connector.
[0019] FIG. 7 is a partial cross-sectional view of a swagable
high-pressure, dual-housing splice connector having machined teeth
in the swaging regions.
[0020] FIG. 8 is a schematic diagram summarizing methodology and
variables of the present invention.
[0021] FIG. 9 is a graph of diffusion coefficients in polyethylene
of phenylmethyldimethoxysilane and oligomeric condensation products
thereof as a function of temperature.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The present invention is directed to a method for selecting
formulations to treat electrical cables. However, before discussing
that method, an inventive method used for enhancing the dielectric
properties of an in-service electrical power cable segment having a
central stranded conductor, usually surrounded by a semi-conducting
strand shield, and encased in a polymeric insulation, with an
interstitial void volume in the region of the conductor, which is
the preferred method for applying the formulations selected using
the method of the present invention, will be discussed in detail.
The method for enhancing the cable segment involves filling the
interstitial void volume with at least one dielectric
property-enhancing fluid at a pressure below the elastic limit of
the polymeric insulation jacket, and subsequently confining the
dielectric property-enhancing fluid within the interstitial void
volume at a desirable sustained residual pressure imposed along the
entire length of the cable segment and, again, below the elastic
limit. The method for enhancing the cable segment exploits the
discovery that, when the interstitial void volume of a cable
segment is filled with a dielectric property-enhancing fluid and
the fluid confined therein at a high residual pressure, the volume
of fluid actually introduced significantly exceeds the volume
predicted from a rigorous calculation of the cable's expansion at
the imposed pressure. The difference between the observed and
calculated volume change increases with pressure and is believed to
be due mainly to the accelerated adsorption of the fluid in the
conductor shield as well as transport thereof through the conductor
shield and insulation of the cable. Thus, with sufficient residual
sustained pressure, it is possible to expand the insulation jacket
of an in-service cable segment in a manner that is so slight as to
not cause any mechanical damage to the cable or to induce any
untoward electrical effects, yet large enough to significantly
increase the volume of dielectric property-enhancing fluid which
can be introduced. As a result, and unlike the prior art, the
present method does not require the above mentioned "soak" period,
and the associated external pressure reservoir, to introduce a
sufficient amount of fluid to effectively treat the cable segment.
As used herein, the term "elastic limit" of the insulation jacket
of a cable segment is defined as the internal pressure in the
interstitial void volume at which the outside diameter of the
insulation jacket takes on a permanent set at 25.degree. C. greater
than 2% (i.e., the OD increases by a factor of 1.02 times its
original value), excluding any expansion (swell) due to fluid
dissolved in the cable components. This limit can, for example, be
experimentally determined by pressurizing a sample of the cable
segment with a fluid having a solubility of less than 0.1% by
weight in the conductor shield and in the insulation jacket (e.g.,
water), for a period of about 24 hours, after first removing any
covering such as insulation shield and wire wrap, after the
pressure is released, the final OD is compared with the initial OD
in making the above determination. For the purposes herein, it is
preferred that the above mentioned residual pressure is no more
than about 80% of the above defined elastic limit.
[0023] The in-service cable segment to which the present methods
discussed are generally applied is the type used in underground
residential distribution and typically comprises a central core of
a stranded copper or aluminum conductor encased in a polymeric
insulation jacket. The strand geometry of the conductor defines an
interstitial void volume. As is well known in the art, there is
usually also a semi-conducting polymeric conductor shield
positioned between the conductor and insulation jacket. However,
this shield can also be of a high permittivity material sometimes
utilized in EPR cables. Further, low voltage (secondary) cables do
not employ such a shield. In addition, the cables contemplated
herein often further comprise a semi-conducting insulation shield
covering the insulation jacket, the latter being ordinarily wrapped
with a wire or metal foil grounding strip and, optionally, encased
in an outer polymeric, metallic, or combination of metallic and
polymeric, protective jacket. The insulation material is preferably
a polyolefin polymer, such as high molecular weight polyethylene
(HMWPE), cross-linked polyethylene (XLPE), a filled copolymer or
rubber of polyethylene and propylene (EPR), vinyl acetate or is a
solid-liquid dielectric such as paper-oil. The base insulation may
have compounded additives such as anti-oxidants, tree-retardants,
plasticizers, and fillers to modify properties of the insulation.
Medium voltage, low voltage and high voltage cables are
contemplated herein. As used herein, the term "in-service" refers
to a cable segment which has been under electrical load and exposed
to the elements for an extended period. In such a cable, the
electrical integrity of the cable insulation has generally
deteriorated to some extent due to the formation of water trees, as
described above. It is also contemplated, however, that the method
discussed can be used to enhance the dielectric properties of a new
cable as well as an in-service cable. For the purposes herein,
"sustained pressure" indicates that the fluid is contained or
trapped within a cable segment's interstitial void volume at the
residual pressure after the pressurized fluid source is removed,
whereupon the pressure decays only by subsequent permeation through
the conductor shield and insulation, as described infra. The method
for enhancing the cable segment to be first discussed teaches the
relationship between pressure and the augmented injection volume
under sustained residual pressure and demonstrates the feasibility
of eliminating or reducing the soak phase on cables with small
conductors.
[0024] The above observations were made as follows. Nominal 100
foot long coiled cable segments (1/0, 175 mil, XLPE; cross-linked
polyethylene insulation) were injected with acetophenone at
sustained pressures of 30, 60, 120, 240, and 480 psig (pounds per
square inch, gage) while the segments were immersed in water at
30.degree. C. using novel high-pressure terminal connectors
described infra. At each pressure, the outside diameter (OD) of the
insulation was measured and compared to the OD before the cable was
pressurized (i.e., 0 psig). The changes in the OD were monitored at
each cable end and four individual measurements (two orthogonal
measurements on each end of each cable segment) were averaged at
each pressure, the repeatability of each individual measurement
being approximately +/-2 mils. These increases in OD were plotted
as a function of pressure, but the theoretically expected linear
relationship was not observed due to the relatively high error of
OD measurement at low pressures. Therefore, the high pressure point
(approximately 480 psig) was used to fit a rigorous equation
relating OD change (deflection) to internal pressure of an annulus,
the latter being a very close approximation of the cable's geometry
(e.g., see Jaeger & Cook, Fundamentals of Rock Mechanics,
2.sup.nd edition, p. 135) according to the following equations: 1
Lame ' s parameters G := E 2 ( 1 + v ) G = 8.6 ksi := E v ( 1 + v )
( 1 - 2 v ) = 98 ksi Radial deflection at any radius with internal
pressure only , Ref . Fundamentals of Rock Mechanics , Jaeger &
Cook , 2 nd Ed . , p .135 u ( r ) := - p i a 2 r 2 ( + G ) ( b 2 -
a 2 ) - p i a 2 b 2 2 G ( b 2 - a 2 ) r
[0025] wherein E is the elastic modulus and v is Poison's ratio for
the cable insulation, u (r)=radial deflection at a given radius r,
a=inner radius, b=outer radius, G=shear modulus, .lambda.=Lame's
parameter, p.sub.i=pressure in the interstices, and "ksi" indicates
units in kilo-pounds per square inch. The increase in OD at 480
psig was first determined to be approximately 9.1 mils (1
mil={fraction (1/1000)} in.), or 1.2% of the initial OD of 0.78 in.
The modulus E was adjusted so as to correspond to this measured OD
deflection using the known value of v=0.46 for the insulation (E=19
kpsi). From this, the change of the inner diameter (ID) was
calculated as 18.2 mil. A similar procedure was used to calculate
the change in ID as a function of pressure. Thus, at 480 psig, the
increase in ID created an incremental annular void volume between
the conductor strands and the conductor shield which corresponds to
the introduction of approximately 4.5 pounds of acetophenone per
1000 feet of cable beyond the amount this cable can accommodate at
atmospheric pressure, the latter amount being about 5.2 pounds per
1000 feet including the negligible compressibility of acetophenone.
The resulting hydraulic expansion translates into, e.g., an 87%
increase in total void volume at 480 psig, and it alone could
eliminate the soak phase required by the prior art methods for some
cables having insufficient interstitial void volume (e.g., those
having a ratio of v.sub.1 to v.sub.2 in Table 1 of U.S. Pat. No.
6,162,491 less than unity). The calculated increase in fluid
accommodated as a function of applied pressure for the above cable,
expressed in pounds/1000 feet (lb/kft) of cable and normalized to a
specific gravity (SG) of 1.0, is represented by the lower curve of
FIG. 1.
[0026] In a similar fashion, the actual total volume (weight)
introduced into the cable as a function of pressure was determined
as follows. A 107 foot length of the above mentioned I/O cable was
fitted with the novel high-pressure connector, described infra, at
each terminus. A fluid reservoir and positive displacement pump
were attached to the first connector via a closable valve and
acetophenone was injected into the cable until fluid was observed
to flow from the opposite end while the cable was maintained at
30.degree. C. in a water bath. At this point, a valve attached to
the second connector was closed and pumping was continued until the
pressure reached the desired level (e.g., the above mentioned 480
psig), at which time the valve on the first connector was shut to
contain the pressurized fluid, this sequence taking approximately
15 to 30 minutes for each target pressure. The amount of fluid so
injected into the interstitial void volume of the cable segment was
determined by weighing the reservoir before and after injection as
well as by noting the amount of fluid displaced by the pump, these
two close measurements then being averaged. Of course, any possible
leakage from the cable was ruled out. As above, this measurement
was normalized to SG=1.0 for a 1000 foot cable to provide a basis
for comparison of the various cables samples. Unexpectedly, the
actual total amount of acetophenone which could be introduced into
the interstitial void volume of the above cable at 480 psig was
found to be considerably greater than the above geometrically
predicted value of 87%. For example, when confined within the cable
interior at 480 psig, the incremental amount of this fluid was 9.4
lb/kft greater than the zero pressure value of 5.2 lb/kft, or 180%
of the zero-pressure interstitial volume (weight) and the total
fluid accommodated was 5.2+9.4=14.6 lb/kft at 480 psig. It was
verified that no leakage of fluid took place. Measurements at other
pressures are represented by the upper curve of FIG. 1 (again
normalized to SG=1.0), wherein the difference between the actual
amount accommodated at a given pressure and the amount predicted
from the above describe geometric calculations is termed the
"Permeation-Adsorption Gap." This gap widened with increasing
pressure over the range studied.
[0027] The effect of fluid compressibility can be readily estimated
and largely discounted as insignificant in the above experiment.
For example, the compressibility of benzene, a material similar to
acetophenone, is 6.1.times.10.sup.-6 .DELTA.V/V.multidot.psi. At a
nominal pressure of 480 psig, benzene would be compressed only
about 0.3%. Thus, even fluids having high compressibility, such as
silicones, would introduce no more than about 0.5 to 1% of
additional fluid at the maximum pressures contemplated herein, an
amount insignificant relative to the increases observed.
[0028] While not wishing to be limited to any specific mechanism,
it is believed that the above described dramatic increase in
effective interstitial void volume (or injection volume) is due, at
least in part, to the heterogeneous and micro-porous nature of the
conductor shield. This shield is typically a polyolefin polymer
filled with 28-40% carbon black. Carbon black, which is added
primarily to impart semi-conducting properties to the conductor
shield, contains microscopic surface irregularities which make it
an excellent adsorption surface for the dielectric
property-enhancing fluid. It is believed that fluids injected at
high pressure essentially flow through these microscopic surfaces
and channels faster than if they were injected at a lower pressure.
Further it is believed that a substantial portion of the fluid can
be reversibly adsorbed onto the carbon black surface (i.e., into
the conductor shield), thereby providing another reservoir to store
the dielectric property-enhancing fluid.
[0029] Besides the advantage of creating a larger "internal
reservoir," one skilled in the art would recognize another
advantage of this rapid radial transport through the conductor
shield. Rapid delivery of dielectric property-enhancing fluid to
the conductor shield/insulation interface where dielectric
degradation has occurred is a desirable outcome not enjoyed by the
prior art approaches. Rapid increase of dielectric performance is
critical for good reactive injection performance (i.e., treatment
after a cable failure). As discussed above, the elevated injection
pressures occasionally utilized in the prior art are released as
soon as the fluid reaches the far end of the cable segment being
injected. Using this conventional mode of operation, the segment
end adjacent to the pressure source receives a small benefit, but
the distal end receives no benefit since it remains at near ambient
pressure throughout the injection process. By analogy to a chain
which fails at its weakest link, any restoration process which does
not benefit the whole cable segment provides virtually no benefit
since a cable failure anywhere along the length causes the entire
length to become non-functional. Again, the low to moderate
pressures used in the art today (10-350 psig) are lower than the
maximum pressures contemplated by the present method (i.e., up to
about 1000 psig) and, most significantly, are bled to near zero
(e.g., nominal soak pressure less than 30 psig and more typically
less than 10 psig, using an external reservoir) after the fluid has
flowed the length of the cable. Thus, for example, while the above
mentioned I/O cable segment having a length of 100 to 300 feet can
be injected in only about 10 to 30 minutes to raise the
interstitial pressure throughout to 480 psig, the present method
holds such pressures throughout the entire cable length for days,
or weeks, or months after the injection is complete.
[0030] Another advantage of the method for enhancing the cable
segment first being discussed is that it accelerates the diffusion
of the dielectric property-enhancing fluid through the insulation
jacket of the cable segment, this being verified as follows. In a
manner similar to the above described experiments, three identical
I/O cable segments having lengths ranging from approximately 105.5
to 107 feet were injected with acetophenone at 30, 240, and 480
psig at 30.degree. C. After the cables were filled, pressure was
maintained for 30 minutes to simulate a typical injection condition
contemplated by the present method. After the 30 minute interval,
the fluid feed was terminated by closing a valve at the feed point
to the cable and the respective pressure was allowed to decay with
time as fluid permeated out of the interstitial volume and into the
conductor shield and insulation (but not by leaking from the
connectors). The results of that pressure decay for only the two
higher pressures are plotted in the FIG. 2, the decay for the 30
psig cable being very rapid and reaching approximately 0 psig
within about one day. Again, while not wishing to be constrained by
any particular theory, it is believed that the initial rapid
decrease of pressure, which was more rapid with greater applied
pressure, results from the transport of fluid from the interstices
into the conductor shield. After this rapid, initial phase, and as
the conductor shield becomes saturated with the fluid, the pressure
decays at a considerably reduced rate. This phase is believed to be
due to the permeation of additional fluid out of the interstitial
void volume and into the insulation.
[0031] In the above experiments, the novel high-pressure connector
250, shown in cross-sectional view in FIG. 3, was used to fill the
test cables at elevated pressure. In a typical assembly and test
procedure, the cable termination was prepared by cutting back the
outermost layers of the I/O cable to expose insulation jacket 12,
per the manufacture's recommendations. Likewise, insulation jacket
12 and associated conductor shield (not shown) were cut back
slightly beyond the manufacturer's requirements to expose stranded
conductor 14 and assure that there was at least a 0.25 inch gap
between termination crimp connector 252 and the wall of insulation
jacket 12 after termination crimp connector 252 was crimped to the
conductor 14. After the crimping procedure was complete, a first
threaded cap 210 was installed over the insulation jacket 12
followed by first aluminum washer 212, rubber washer 214, and a
second aluminum washer 212. The cable-side threaded housing 220 was
then loosely threaded onto the already installed first threaded cap
210 at the right side of high-pressure terminal connector 250. The
rubber O-ring 216 was installed in a groove of the termination-side
threaded housing 218 and the latter was, in turn, threaded onto the
cable-side threaded housing 220 until the external gap between the
two housing components was essentially closed. It should be
apparent to someone with ordinary skill that housings 218 and 220
could be reversed in the above description with no impact. An
aluminum washer 226, having associated set screws 228 and
illustrated in detail in FIG. 3A, was slid into position so as to
reside over the smooth surface of termination crimp connector 252.
While the assembly up to this point was slid slightly toward the
cable side, two or three set screws were engaged so that aluminum
washer 226 was immobilized with respect to the termination crimp
connector 252. The position was chosen so that the rubber washer
224, which was added next, fell squarely on the un-crimped
cylindrical surface of termination crimp connector 252 when the
assembly was completed. At this point, the partially assembled
high-pressure connector could be slid back toward the termination
side to the position shown in FIG. 3. Aluminum washer 222 was
placed adjacent to the rubber washer 224, a second threaded cap 210
was mated with the termination-side threaded housing 218 and
threaded tightly thereto. The resulting compression provided
sufficient force to deform rubber washer 224 to make a fluid-tight
seal with respect to termination crimp connector 252 and the inside
diameter of the termination-side threaded housing 218. The threads
on the cable-side housing 220 were then tightened firmly such that
the rubber washer 214 was compressed between the two aluminum
washers 212, the compression providing sufficient force to deform
rubber washer 214 to make a fluid-tight seal with respect to the
surface of insulation jacket 12 and the inner peripheral surface of
the cable-side threaded housing 220.
[0032] A split ring clamping collar 230, comprising two halves 232
and 234, each half having course internal threads 231 for engaging
and grasping insulation jacket 12, was placed in the approximate
position shown in FIG. 3 and in perspective view in FIG. 4. A hose
clamp was used to temporarily hold the two halves of the collar 230
in place while two clamping collar bolts 238 were inserted and
threaded into the first threaded cap 210 and partially tightened.
The hose clamp was then removed and two clamping collar chord bolts
241 were screwed tightly into place to permanently join the two
halves 232 and 234 of clamping collar 230, and collar bolts 238
were then completely tightened. As a result, the rough threads 231
disposed on the inner diameter of collar 230 partially penetrated
or deformed the surface of insulation 12 so as to provide
resistance to axial movement of connector 250 relative to the
insulation jacket 12 of the cable segment to be injected under
pressure. It was previously determined that, without such a means
for securing the insulation jacket to the high-pressure connector,
a "pushback" phenomenon resulted. Pushback is defined herein as the
axial movement or creep of the insulation jacket and conductor
shield away from the cut end (crimped end) of the conductor of a
cable segment when a fluid is confined within its interstitial void
volume at a high residual pressure. Ultimately, this pushback
phenomenon resulted in sufficient displacement of the insulation
jacket 12 relative to the above described compression seal
212/214/212 to cause fluid to leak from the connection and the high
residual pressure to quickly collapse, thereby destroying the
intent of the instant method. Acetophenone was then injected or
withdrawn through one of the threaded injection ports 240 or 242
using an NTP to tube fittings well known in the art, as described
above. The unused threaded injection port was plugged with a
threaded plug (not shown). The inventors of the instant application
developed the above-described high-pressure power cable connector
and other connectors for use with the method for treating
electrical cables at sustained elevated pressure described herein.
Such high-pressure connectors are described in detail in
Provisional patent application Method for Treating Electrical Cable
at Sustained Elevated Pressure, Ser. No. 60/549,322, filed Mar. 1,
2004 and a Nonprovisional patent application entitled High-Pressure
Power Cable Connector filed concurrently herewith, which are
incorporated herein by reference in their entirety.
[0033] The actual permeation rate of a dielectric
property-enhancing fluid through the insulation jacket is dependent
on the fluid pressure in the cable interstices and rapid increases
in dielectric performance can be imparted with higher, sustained
pressures. To illustrate this benefit according to the present
method, the following dielectric property-enhancing fluid mixtures
were prepared: FLUID 1=25% (weight) acetophenone+75% (weight)
p-tolylethylmethyldimethoxysilane; FLUID 2=25% (weight)
acetophenone+75% (weight) vinylmethylbis(1-phenylethyleneoxy)sil-
ane (i.e., methylvinyl bis (1-phenyl ethenyloxy)silane). Using the
novel high-pressure connectors, described above, each fluid mixture
was injected into the interstitial void volume of a 220-foot coiled
segment of 1/0, 175 mil XLPE cable at 480 psig, and contained
therein without leaking, according to the present method. This
cable had been previously aged several years in an ambient
temperature water tank while a voltage of 2.5U.sub.0 (i.e.,
2.5.times.rated voltage) was applied thereto. The coils were
immersed in a water bath at a controlled temperature of 25.degree.
C. After injection, but while the latent pressure was maintained on
the coils by suitable injection devices and valving, a voltage of
21.65 kV (i.e., 2.5.times.rated voltage) was applied. After 7 days,
each cable was removed from the water bath and promptly cut into 6
samples for AC breakdown testing according to ICEA S-97-682-2000
10.1.3 "High Voltage Time Test Procedure," wherein the key test
parameters were: 49-61 Hz, room temperature, 100 v/mil for 5
minutes raised in 40 v/mil increments each 5 minutes to failure.
Before treatment, a third identically aged sample was sacrificed to
establish the baseline performance for the laboratory aged cable.
The results of testing were plotted on Weibull graphs. The 63.3%
probability breakdown value increased from 370 volts/mil for the
aged cable to 822 volts/mil for the segment treated with FLUID 1
(i.e., a 2.22 fold or 122% improvement over the control).
Similarly, the 63.3% probability breakdown value increased from 370
volts/mil (control) to 999 volts/mil for the segment treated with
FLUID 2 (i.e., a 2.7 fold or 170% improvement over the control). In
each case, the 90% confidence bounds for the Weibull curves were
quite narrow at the 63.3% industry recognized standard. These
results stand in sharp contrast to a very similar experiment using
the prior art approach (see above cited "Entergy Metro Case Study")
wherein CableCURE.RTM./XL fluid was injected into a 25 kV, 750
kcmil cable at pressures of 30 and 117 psig. CableCURE/XL fluid is
described in U.S. Pat. No. 5,372,841 and an MSDS sheet as a mixture
of 70% phenylmethyldimethoxysilane (which has a diffusion
coefficient of 5.73.times.10.sup.-8 cm.sup.2/sec at 50.degree. C.)
and 30% trimethylmethoxysilane (which has a diffusion coefficient
of 2.4.times.10.sup.-7 cm.sup.2/sec at 50.degree. C.) and is thus
analogous to the above fluid mixtures with respect to the relative
concentrations of rapidly diffusing components and slower diffusing
components as well as the absolute values of the diffusion
coefficients of the former. In this study, the reported 63%
breakdown value of the treated cables relative to control increased
only 14.5% and 34.6% in seven days for the 30 psig and 117 psig
treated cables, respectively. It is thus seen that, in absolute
terms, the present method using the average performance of the
above restorative fluid mixtures provides a (822+999)/2-370=541
volts/mil improvement. At best, this prior art employing a
non-sustained pressure treatment provided an improvement of 74.7
kV/262 mil-55.5 kV/262=28-212=73 volts/mil, wherein 262 mils is the
thickness of the 25 kV cable's insulation. Put another way, the
present method provides an improvement of at least about 640% over
the old technology with respect to AC breakdown performance over a
one week period.
[0034] In one embodiment of the method for enhancing the cable
segment first being discussed, the interstitial void volume of a
cable segment is injected (filled) with at least one dielectric
property-enhancing fluid. As used herein with respect to the
methods being discussed, a cable segment is generally either a
length of continuous electrical cable extending between two
connectors used in the injection of one or more dielectric
property-enhancing fluid into the length of cable therebetween, or
a length of electrical cable extending between two such connectors
with one or more splice or other style connectors therebetween
operation in a flow-through mode. The actual pressure used to fill
the interstitial void volume is not critical provided the
above-defined elastic limit is not attained. After the desired
amount of the fluid has been introduced, the fluid is confined
within the interstitial void volume at a sustained residual
pressure greater than 50 psig using the aforementioned two
connectors defining the cable segment, but below the elastic limit
of the insulation jacket. It is preferred that the residual
pressure is between about 100 psig and about 1000 psig, most
preferably between about 300 psig and 600 psig. Further, for the
method for enhancing the cable segment first being discussed, it is
preferred that the injection pressure is at least as high as the
residual pressure to provide an efficient fill of the cable segment
(e.g., 550 psig injection and 500 psig residual). In another
embodiment thereof, the residual pressure is sufficient to expand
the interstitial void volume along the entire length of the cable
segment by at least 5%, again staying below the elastic limit of
the polymeric insulation jacket. Optionally, the dielectric
property-enhancing fluid may be supplied at a pressure greater than
about 50 psig for more than about 2 hours before being contained in
the interstitial void volume.
[0035] In another embodiment, the method for enhancing the cable
segment first being discussed may be applied to a cable segment
having a first closable high-pressure connector attached at one
terminus thereof and a second closable high-pressure connector
attached at the other terminus thereof, each connector providing
fluid communication with the interstitial void volume of the
segment. Each connector employs an appropriate valve to open or
close an injection port, as further described below. A typical
sequence comprises initially opening both valves and introducing at
least one dielectric property-enhancing fluid via the port of the
first connector so as to fill the interstitial void volume of the
segment. At this point, the valve of the second connector is closed
and an additional quantity of the fluid is introduced via the port
of the first connector under a pressure P greater than 50 psig.
Finally, the valve of the first connector is closed so as to
contain the fluid within the void volume at a residual pressure
essentially equal to P.
[0036] Regardless of any particular embodiment, it is preferred
that the dielectric property-enhancing fluid be selected such that
the residual pressure decays to essentially zero psig in greater
than 2 hours, but preferably in more than 24 hours, and in most
instances within about two years of containing the fluid, as
discussed supra with respect to FIG. 2. Furthermore, since the
instant method can supply an additional increment of fluid to the
interstitial void volume, it is also contemplated the method can be
used to advantage to treat cable segments wherein the weight of the
dielectric property-enhancing fluid corresponding to the
interstitial void volume is less than the weight of the fluid
required to saturate the conductor shield and the insulation jacket
of the segment (i.e., a desirable amount for optimal treatment).
Thus, the method for enhancing the cable segment first being
discussed is particularly advantageous when applied to the
treatment of round or concentric stranded cables having a size of
no greater than the above mentioned 4/0 (120 mm.sup.2), of
compressed stranded cables having a size of no greater than 250 kcm
(225 mm.sup.2), and of compact stranded cables having a size of no
greater than 1000 kcm (500 mm.sup.2).
[0037] In view of the above mentioned pushback phenomenon, special
connectors which are appropriately secured to the insulation jacket
of the cable are preferably used to facilitate the instant method.
Such connectors, as exemplified by the above described
high-pressure terminal connector of FIG. 3 and further described
below, employ either external or integral valves which allow fluid
to be introduced into the cable segment as well as confined at the
residual high pressure. Such a valve can also serve to withdraw
water and/or contaminated fluid from the other, remote end of the
cable segment. For example, in the connector shown in FIG. 3, at
least one injection port is fitted with an external
quick-disconnect coupling such that, after injection, the
pressurized fluid supply can be readily disconnected and the
injected fluid trapped within the connector housing and the
interstitial volume of the cable at a residual pressure P
throughout the entire length of the cable segment being treated. It
is preferred that miniaturized versions of conventional
quick-disconnect couplings are used and that these fit essentially
flush with the outer surface of the housing to provide a
protrusion-free or low profile outer surface for the high-pressure
splice connector to readily receive subsequent insulation
component(s) and avoid any sharp electrical stress concentration
points. Other preferred high-pressure connectors which may
advantageously be utilized in the practice of the present method
are described below with reference to the drawings illustrating
exemplary embodiments thereof, wherein the same reference numerals
are applied to identical or corresponding elements.
[0038] A swagable high-pressure terminal connector 81 which may be
used in the instant method is shown in FIG. 5. The housing 80,
having internal machined teeth 32, is sized so that its ID (inner
diameter) is just slightly larger than the OD (outer diameter) of
insulation jacket 12 and is configured to receive the end portion
of cable segment 10 therein. Housing 80 is integral with a
termination crimp connector portion 82. In application, the
termination crimp connector portion 82 is crimped to conductor 14
of cable 10 at an overlapping region to secure it thereto and
provide electrical communication therewith. Housing 80, further
comprises a self closing spring-actuated valve 36 (illustrated in
enlarged detail in FIG. 6) disposed at injection port 48 for
introduction of the dielectric property-enhancing fluid. After
housing 80 is placed in the position shown in FIG. 5, a swage is
applied to the periphery of housing 80 over circumferential teeth
32 such that teeth 32 deform and partially penetrate insulation
jacket 12 along a periphery thereof sufficiently so as to
simultaneously form a fluid-tight seal against the insulation
jacket and prevent pushback (as described above) of the insulation
jacket when the cable segment is subjected to sustained interior
pressure.
[0039] As used herein, swaging or "circumferential crimping" refers
to the application of radial, inwardly directed compression around
the periphery of the housing over at least one selected axial
position thereof. This swaging operation produces a circular
peripheral indented region (e.g., a groove or flat depression) on
the outer surface of the housing and inwardly projects a
corresponding internal surface thereof into the insulation jacket
(or bushing or splice crimp connector) so as to partially deform
the latter at a periphery thereof. Swaging can be accomplished by
methods known in the art, such as a commercially available
CableLok.TM. radial swaging tool offered by Deutsch Metal
Components, Gardena, Calif. Swaging is to be distinguished from a
normal crimping operation, wherein one-point (indent crimp),
two-point or multi-point radial crimps are applied to join crimp
connectors using tools well known in the art (e.g., the crimp
connectors attached to the conductor). The resulting crimp from
such a single or multi-point crimping operation is referred to
simply as "crimp" herein and may be accomplished with shear
bolts.
[0040] The injection valve 36 used in the above high-pressure
swagable terminal connector (FIG. 5) is an example of an integral
valve and is illustrated in detail in FIG. 6. A hollow injection
needle 42 having side port(s) 46 and injection channel 44 is shown
in position just prior to injecting a pressurized fluid. Needle 42
includes a concave portion at its tip which mates with a
corresponding convex profile 90 on plug-pin 86, the latter being
attached to C-shaped spring 34, which rides on a peripheral inner
surface of housing 80 and preferably within a slightly indented
channel in the latter. This mating with the needle tip assures that
a plug-pin 86 carried by the C-shaped spring 34 is centered in, and
just displaced from, injection port 48 while needle 42 is inserted
and likewise centers the plug-pin 86 in the injection port 48 of
housing 80 as the needle 42 is withdrawn. The convex and concave
surfaces could, of course, be reversed and other shapes could be
utilized to achieve the same effect. The plug-pin 86 and an O-ring
88 with the plug-pin to extending therethrough, in combination
provide a fluid-tight seal when the needle tip is withdrawn and
C-shaped spring 34 presses against O-ring 88 so as to deform the
latter into a slight saddle shape, whereby the O-ring 88 seats
against the inside surface of the housing 80 and the outside
surface of C-shaped spring 34. It will be appreciated that, as the
pressure within the housing 80 increases, the compressive force on
the O-ring 88 increases and thereby improves the sealing
performance of O-ring 88. In practice, a clamp assembly (not shown)
which houses needle 42 is mounted over injection port 48 to form a
fluid-tight seal to the exterior of housing 80. As the tip of
needle 42 is actuated and inserted into injection port 48, thereby
depressing plug-pin 86 and unseating O-ring 88, fluid can be
injected into or withdrawn from the interior of housing 80 through
needle 42.
[0041] A preferred dual-housing, swagable high-pressure splice
connector 101, which can be assembled from two identical swagable
high-pressure terminal connectors, is illustrated in FIG. 7. In a
typical assembly procedure using this embodiment, described here
for one of the two cable segments 10 shown in FIG. 7, the
insulation jacket 12 is first prepared for accepting a splice crimp
connector 18, as described above. A housing 100, which includes
injection port 48, is sized such that its larger ID at one end
portion is just slightly larger than the OD of insulation jacket 12
and its smaller ID at an opposite end portion is just slightly
larger than the OD of splice crimp connector 18. The housing 100 is
slid over the corresponding conductor 14 and insulation jacket 12,
and the splice crimp connector 18 is then slipped over the end of
the conductor 14 and within the housing. Preferably, the lay of the
outermost strands of conductor 14 of the cable segment 10 is
straightened to an orientation essentially parallel to the axis of
the cable segment 10 to facilitate fluid flow into and out of the
respective interstitial volume, as well known in the art. Housing
100, having O-ring 104 residing in a groove therein, is swaged with
respect to splice crimp connector 18. The swage is applied at
position 102 over the O-ring 104 and the machined teeth 108, which
may have a profile varying from roughly triangular to roughly
square. This swaging operation joins the conductor 14, splice crimp
connector 18, and housing 100 in intimate mechanical, thermal and
electrical contact and union, and provides a redundant seal to the
O-ring 104. Swaging can be performed in a single operation, as
described above, or in phases (i.e. wherein splice crimp connector
18 is first swaged together with conductor 14, and then housing 100
is swaged with the splice crimp connector/conductor combination
18/14, provided that the length of the splice crimp connector and
length of the housing can accommodate sliding housing 100 out of
the way or in the unusual event that the splice crimp connector OD
is greater than the insulation OD (e.g., as sometimes found in
Japan). In either event, this swaging assures intimate mechanical,
thermal and electrical contact and union between housing 100,
splice crimp connector 18 and conductor 14; it also results in a
fluid-tight seal between housing 100 and splice crimp connector 18.
When the splice according to this embodiment is to be used in a
flow-through mode, water stop region 106 (i.e., a barrier wall
within splice crimp connector 18) may be omitted or drilled out
prior to assembly. To facilitate flow through the swaged conductor
area, at least one micro tube (not shown) of sufficiently high
strength to avoid crushing during subsequent swaging and of
sufficient length to allow fluid communication between the annular
spaces remaining at each end of the crimp connector 18, may be
placed within the annulus formed between the two conductors 14 and
the crimp connector 18 when the water stop region 106 is omitted. A
swage is then applied to the exterior of housing 100 over machined
teeth 32 such that teeth 32 deform insulation jacket 12
sufficiently to form a fluid tight seal and prevent pushback of the
insulation jacket when the cable segments are pressurized. The
injection port 48 on housing 100 allows fluid to be injected or
withdrawn at elevated pressures employing a valve 36 of the type
described in FIG. 6 above. When the swagable high-pressure splice
connector according to this embodiment is to be used in a
flow-through mode, the injection ports may be omitted.
[0042] The above high-pressure connectors allow two cable segments
to be injected simultaneously using appropriate fitting(s) and
injection port(s). Alternatively, two (or more) segments can be
injected sequentially starting at an end of the first segment
distal to the high-pressure splice connector, through the
high-pressure splice connector and then through the second segment
(flow-through mode). In this, and any other so-called flow-through
mode, the injection port(s) may be eliminated.
[0043] In general, the components of the high-pressure connectors,
except for any rubber (elastomeric) washers or rubber O-rings
employed, are designed to withstand the anticipated pressures and
temperatures and may be fabricated from a metal such as aluminum,
aluminum alloy, copper, beryllium-copper, or stainless steel. It is
also possible to employ non-conductive components if the
high-pressure terminal or splice connector design accommodates
electrical communication between the associated termination crimp
connector or splice crimp connector (i.e., with the conductor in
each case) and any subsequently applied conductive insert. That is,
the semi-conductor portion of any termination or splice body
applied over the high-pressure terminal connector or splice
connector, as conventionally practiced in the art, should be
essentially at the same electrical potential as the conductor.
Preferably, thick aluminum or copper washers, in conjunction with
rubber washers are used in connectors employing compression seals,
as illustrated in FIG. 3. Since these metals exhibit high thermal
conductivities, they facilitate dissipation of heat in the
load-carrying termination or splice, thereby reducing the
temperature at the surface of the insulation jacket proximal to the
respective connector. Rubber washers and O-rings may be formed from
any suitable elastomer compatible with the fluid(s) contemplated
for injection as well as the maximum operating temperature of the
connector. Preferred rubbers include fluorocarbon rubbers,
ethylene-propylene rubbers, urethane rubbers and chlorinated
polyolefins, the ultimate selection being a function of the
solubility of, and chemical compatibility with, the fluid(s) used
so as to minimize swell or degradation of any rubber component
present. It is contemplated that any high-pressure splice or
dead-front terminal connector provides for electrical contact
between the respective splice crimp connector or dead-front
termination crimp connector and the corresponding conductive
insert, as commonly practiced in the art, in order to prevent
electrical discharges or corona. In addition, it is preferred that
there be good thermal contact between the conductor and the housing
(e.g., using set screws, crimping) to provide for heat dissipation
away from the conductor.
[0044] As will be apparent to those skilled in the art, a
high-pressure splice connector is generally symmetrical with
respect to a plane perpendicular to the cable axis and through the
center of the splice crimp connector, and the assembly procedures
described are applied to both ends of the splice. It also will be
recognized that different combinations of sealing and securing
options, such as illustrated herein, may be combined in
"mix-and-match" fashion to provide the intended sealing and
securing functions, although the skilled artisan will readily
determine the more desirable and/or logical combinations.
[0045] In general, the dielectric property-enhancing fluid used
(also referred to a tree retardant agent or anti-treeing agent
herein) may be selected from any of the compounds known in the art
to prevent water trees in polymeric insulation when compounded into
the insulation material and/or injected into a new or an in-service
cable. Such compounds as aromatic ketones (e.g., acetophenone),
fatty alcohols (e.g., dodecanol), UV stabilizers (e.g.,
2-ethylhexyltrans-4-methoxycinnamate), and organoalkoxysilanes,
illustrate the range of compounds which can be employed as the
dielectric-enhancing fluid in the present method. Many such
compounds have been described in the patent literature and the
interested reader is referred to U.S. Pat. No. 4,144,202 to
Ashcraft et al., U.S. Pat. No. 4,212,756 to Ashcraft et al., U.S.
Pat. No. 4,299,713 to Maringet et al., U.S. Pat. No. 4,332,957 to
Braus et al., U.S. Pat. No. 4,400,429 to Barlow et al., U.S. Pat.
No. 4,608,306 to Vincent, U.S. Pat. No. 4,840,983 to Vincent, U.S.
Pat. No. 4,766,011 to Vincent et al, U.S. Pat. No. 4,870,121 to
Bamji et al., U.S. Pat. No. 6,697,712 to Bertini et al. and U.S.
Pat. No. 5,372,841 to Kleyer et al., among others.
[0046] According to the method for selecting formulations to treat
electrical cables to be more specifically discussed below, it is
contemplated that the dielectric property-enhancing fluid may be a
mixture of two or more fluids of the type describe herein, provided
that such a mixture remains fluid under the conditions of the
actual injection. Specific, non-limiting, examples of suitable
dielectric property-enhancing materials may be selected from one or
more of the following:
[0047] phenylmethyldimethoxysilane
[0048] phenyltrimethoxysilane
[0049] diphenyldimethoxysilane
[0050] phenylmethyldiethoxysilane
[0051] trimethylmethoxysilane
[0052] acetonitrile
[0053] benzonitrile
[0054] tolyinitrile
[0055] t-butyldiphenylcyanosilane
[0056] 1,3-bis(3-aminopropyl)tetramethyldisiloxane
[0057] 1,4-bis(3-aminopropyldimethylsilyl)benzene
[0058] 3-aminopropylpentamethyldisiloxane
[0059] aminomethyltrimethylsilane
[0060] 1,4-bis(3-aminopropyldimethylsilyl)benzene
[0061] 3-aminopropylmethylbis(trimethylsiloxy)silane
[0062] (4-bromophenylethynyl)trimethylsilane
[0063] p-chlorophenyltrimethylsilane
[0064] bis(cyanopropyl)tetramethyldisiloxane
[0065] 4-aminobutyltriethoxysilane
[0066] bis(3-cyanopropyl)dimethoxysilane
[0067] N-methylaminopropylmethyldimethoxysilane
[0068]
N-(3-methacryloxy-2-hydroxypropyl)-3-aminopropyltriethoxysilane
[0069] N-ethylaminoisobutyltrimethoxysilane
[0070] 3-(2,4-dinitrophenylamino)propyltriethoxysilane
[0071] N,N-dimethylaminopropyl)trimethoxysilane
[0072] (N,N-diethyl-3-aminopropyl)trimethoxysilane
[0073] N-butylaminopropyltrimethoxysilane
[0074] bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane
[0075] 3-aminopropyltris(methoxyethoxyethoxy)silane
[0076] 3-aminopropyltrimethoxysilane
[0077] 3-aminopropylmethyldiethoxysilane
[0078] 3-aminopropyldimethylethoxysilane
[0079] p-aminophenyltrimethoxysilane
[0080] m-aminophenyltrimethoxysilane
[0081] 3-(m-aminophenoxy)propyltrimethoxysilane
[0082] aminomethyltrimethylsilane
[0083] N-(2-aminoethyl)-11-aminoundecyltrimethoxysilane
[0084] N-(6-aminohexyl)aminopropyltrimethoxysilane
[0085] N-(2-aminoethyl)-3-aminopropyltrimethoxysilane
[0086] N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane
[0087] N-(2-aminoethyl)-3-aminoisobutylmethyldimethoxysilane
[0088] 3-(N-allylamino)propyltrimethoxysilane
[0089] 11-cyanoundecyltrimethoxysilane
[0090] 2-cyanoethyltrimethoxysilane
[0091] 2-cyanoethyltriethoxysilane
[0092] 2-cyanoethylmethyldimethoxysilane
[0093] (3-cyanobutyl)methyldichlorosilane
[0094] bis(3-cyanopropyl)dimethoxysilane
[0095] 3-(triethoxysilylpropyl)-p-nitrobenzamide
[0096] 2-(diphenylphosphino)ethyltriethoxysilane
[0097] 3-cyanopropylphenyldimethoxysilane
[0098] bis(3-cyanopropyl)dimethoxysilane
[0099] phenyltris(methylethylketoximio)silane
[0100] vinylmethylbis(methylethylketoximino)silane
[0101] vinyltris(methylethylketoximino)silane
[0102] phenylmethylbis(dimethylamino)silane
[0103] phenethyldimethyl(dimethylamino)silane
[0104] n-octyldiisopropyl(dimethylamino)silane
[0105] n-octadecyldimethyl(dimethylamino)silane
[0106] bis(dimethylamino)vinylmethylsilane
[0107] bis(dimethylamino)vinylethylsilane
[0108] bis(dimethylamino)diphenylsilane
[0109] vinyltris(methylethylketoximino)silane
[0110] vinylmethylbis(methylethylketoximino)silane
[0111] phenyltris(methylethylketoximio)silane
[0112] phenyloctyidialkoxysilane
[0113] dodecylmethyldialkoxysilane
[0114] n-octadecyldimethylmethoxysilane
[0115] n-decyltriethoxysilane
[0116] dodecylmethyldiethoxysilane
[0117] dodecyltriethoxysilane
[0118] hexadecyltrimethoxysilane
[0119] 1,7-octadienyltriethoxysilane
[0120] 7-octenyltrimethoxysilane
[0121] 2-(3-cyclohexenyl)ethyl]trimethoxysilane
[0122] (3-cyclopentadienylpropyl)triethoxysilane
[0123] 21-docosenyltriethoxysilane
[0124] (p-tolylethyl)methyldimethoxysilane
[0125] 4-methylphenethylmethyldimethoxysilane
[0126] divinyldimethoxysilane
[0127] o-methyl(phenylethyl)trimethoxysilane
[0128] styrylethyltrimethoxysilane
[0129] (chloro p-tolyl)trimethoxysilane
[0130] p-(methylphenethyl)methyldimethoxysilane
[0131] 2-hydroxy-4-(3-triethoxysilylpropoxy)diphenylketone
[0132] dimesityldimethoxysilane
[0133] di(p-tolyl))dimethoxysilane
[0134] (p-chloromethyl)phenyltrimethoxysilane
[0135] chlorophenylmethyldimethoxysilane
[0136] SF.sub.6 (sulfur hexafluoride)
[0137] fluorocarbons or halocarbons
[0138] chlorophenyltriethoxysilane
[0139] phenethyltrimethoxysilane
[0140] phenethylmethyldimethoxysilane
[0141] N-phenylaminopropyltrimethoxysilane
[0142] (aminoethylaminomethyl)phenethyltriethoxysilane
[0143] 3-cyanopropylmethyldimethoxysilane
[0144] methylphenyl bis (1-phenyl ethenyloxy)silane
[0145] methylvinyl bis (1-phenyl ethenyloxy)silane
[0146] Thus, for example, the fluid may be a mixture of the type
disclosed in U.S. Pat. No. 5,372,841 comprising (A) at least one
antitreeing agent; and (B) a water-reactive compound, the
water-reactive compound having a diffusion coefficient of greater
than 10.sup.-7 cm.sup.2/second at 50.degree. C. in the polymeric
insulation and the mixture having an initial viscosity of
.ltoreq.100 cP at 25.degree. C., and wherein (A) and (B) are
different. A particular fluid of this type is a mixture an
aryl-functional alkoxysilane, such as phenylmethyldimethoxysilane
or phenyltrimethoxysilane, and a water-reactive compound selected
from trimethylmethoxysilane or dimethyldimethoxysilane.
[0147] A preferred dielectric property-enhancing fluid is a mixture
containing at least one component having a permeability of less
than 10.sup.-10 g/second-cm at 25.degree. C. in the insulation
polymer and containing no more than two water-reactive groups in
each molecule. The above component has a dielectric constant which
is at least twice that of the polymeric insulation. An example of
such a component is a cyanoalkoxysilane which can have the
formula
R.sub.xR'.sub.ySi(OR").sub.z
[0148] wherein x=1 or 2, y=0 or 1, z=1, 2 or 3, and x+y+z=4, and
wherein R is a cyano-containing organic group having 3-13 carbon
atoms, R' is an organic group having 1 to 3 carbon atoms,
preferably a hydrocarbon group, and OR" is a water-reactive group
selected from an alkoxy group having 1 to 3 carbon atoms or an enol
ether group. Preferably x=1, y=1, z=2, R is selected from isomers
of cyanobutyl, cyanopropyl or cyanoethyl groups, R' is methyl, and
OR" is a methoxy group. Specific cyano-containing alkoxysilanes
include cyanoethylmethyldimethoxysilane,
cyanopropylmethyldimethoxysilane and
cyanobutylmethyldimethoxysilane, inter alia.
[0149] It is also preferred that the dielectric property-enhancing
fluid is a mixture of acetophenone with one or more of the above
materials, preferably containing less than about 30% (weight) of
the latter. Such compositions containing acetophenone preferably
also include at least one material selected from methylphenyl bis
(1-phenyl ethenyloxy)silane, methylvinyl bis
(1-phenylethyleneoxy)silane, p-tolylethylmethyldimethoxys- ilane,
cyanobutylmethyldimethoxysilane, and
cyanopropylmethyldimethoxysila- ne.
[0150] The unexpected increase in injection volume possible with
the method for enhancing the cable segment first being discussed
(i.e., the above mentioned permeation-adsorption gap) offers
advantages beyond the aforementioned elimination of the soak phase
utilized by the purveyors of the prior art. For example, the
present method allows levels of active ingredients to be supplied
to the cable beyond the equilibrium saturation values suggested by
the prior art. This extra dielectric property-enhancing fluid
provides further flexibility in tailoring treatment fluid
combinations which target short-term reactive performance as well
as preemptive performance (i.e., a preventive treatment for
long-term performance). In each of these cases, the advantages of
reactive and preemptive performance can be realized without the
need to compromise the proactive performance (i.e., treatment for
medium term when cable is statistically likely to fail in near
future) targeted by the prior art approach. Moreover, the total
amount of such a fluid mixture introduced can be easily adjusted by
selecting the injection and residual pressures, according to the
method for enhancing the cable segment first being discussed, to
tailor the injection to the cable owner's economic or technical
requirements. Thus, while it is likely that the short-term
performance of any treatment fluid will benefit from the higher
transport rates described herein, the method also allows the
introduction of an entirely new class of materials which, without
the benefit of the current method, would not diffuse appreciably
into the insulation or could not be efficiently supplied in
sufficient volume to the interstitial void volume. Such a
component, defined herein as a Class S material has a permeability
of less than about 10.sup.-10 g/second-cm at 25.degree. C. as well
as solubility of about 0.0001 to about 0.02 gram/cm.sup.3 at
25.degree. C. or has a diffusivity (diffusion coefficient) of less
than about 10.sup.-8 cm.sup.2/sec at 50.degree. C., each property
being determined in the insulation polymer. The method allows the
use of Class S materials since it accelerates permeation of fluid
into the insulation while the pressure is still high enough to
provide an enhanced driving force and it addresses the above
mentioned observation that many in-service cables present an
inadequate interstitial void volume relative to the volume of fluid
required to treat the cable. The inclusion of such a slowly
diffusing material in the fluid composition being injected is
believed to impart improved long-term (e.g., 10 to 40 years)
performance. If such a Class S material were used in the methods of
the prior art, a corresponding reduction in the amount of
short-term performance materials, medium-term performance
materials, or both, would have to be made. In the former case it is
unlikely that the inadequately treated cable would provide reliable
performance for the time required to recognize any benefits from
the low diffusivity materials. In the alternative, the costly and
dangerous soak phase would have to be greatly extended, this option
being effectively prohibited by the safety and economic
implications.
[0151] It is therefore preferred that at least two classes of
materials, and more preferably three classes, are combined to
provide the dielectric property-enhancing fluid. Optimum amounts
and optimum ratios of such components are selected based on the
specific geometry of the cable being treated and the performance
characteristics desired by the circuit owner. These three classes
are defined as follows, wherein each property is measured in the
cable insulation material at the indicated temperature:
[0152] Class Q--Quickly diffusing materials having a diffusion
coefficient greater than about 10.sup.-7 cm.sup.2/sec at 50.degree.
C., such as acetophenone and trimethylmethoxysilane or other high
diffusivity materials disclosed in the above cited U.S. Pat. No.
5,372,841. Such materials impart short-term performance (reactive
performance) (generally, 0 to about 12 months).
[0153] Class M--Moderately diffusing materials having a diffusion
coefficient greater than about 10.sup.-8 cm.sup.2/sec, but less
than about 10.sup.-7 cm.sup.2/sec at 50.degree. C., such as
phenylmethyldimethoxysilane and p-tolylethylmethyldimethoxysilane.
Such materials impart medium-term performance (proactive
performance) (generally about 12 to about 120 months).
[0154] Class S--Slowly diffusing materials or low solubility
materials, as discussed above, having a low solubility of about
0.0001 to about 0.02 gram/cm.sup.3 at 25.degree. C. or having a
diffusivity less than about 10.sup.-8 cm.sup.2/sec at 50.degree.
C., and having a permeability less than about 10.sup.-10
g/cm.multidot.s at 25.degree. C., each property being measured in
the insulation material, such as cyanobutylmethyldimethoxysilane,
cyanoethylmethyldimethoxysilane and
cyanopropylmethyldimethoxysilane. Such materials impart long-term
(preemptive) performance (generally greater than about 120
months).
[0155] For each desired class of material to be employed, the
optimum concentration in the strand shield (conductor shield) and
the insulation jacket are calculated or determined by experiment.
For materials with solubility greater than about 0.02
grams/cm.sup.3 at 25.degree. C. (many Class Q and Cass M materials
fall into this category), this optimum is generally the respective
saturation level at average soil temperature at the depth the cable
is buried, often at about 1 meter. Supply of fluid substantially
above this level has been shown to result in the above described
super-saturation which may be deleterious to the circuit
reliability. In view of the low solubility of Class S materials,
their optimum concentration is generally greater than the
saturation level since there is little chance of damage due to this
phenomenon, and the effective life of the treated cable increases
with the amount of Class S material supplied.
[0156] It is believed that materials of one of the above defined
classes interact little with materials from another class since the
diffusivities between any two classes typically differ by an order
of magnitude. Furthermore, it has been well established in the art
that the solubility of oligomers is substantially less than that of
corresponding monomers. Therefore, damage to a cable due to
supersaturation over long periods of time using constituents which
form oligomers (e.g., organoalkoxysilane reacting with adventitious
water in the cable) is not a concern. Thus, to enjoy the benefits
of short-term, medium-term, and long-term reliability performance,
the present method teaches the following protocol:
[0157] (a) The saturation (or other optimum level) for each
material class (i.e., there may be two or more components within
each material class) is measured (or calculated) in the conductor
shield and insulation. The optimum level (or the minimum optimum
level for low solubility components) should preferably account for
the anticipated average conductor shield and insulation temperature
and the typical temperature cycling (.DELTA.T) over the anticipated
lifetime of the cable.
[0158] (b) The concentration of each class and each component in
the conductor shield, as determined in step (a), is multiplied by
the specific mass of the conductor shield to give the required
weight of the respective class and component therein. Likewise, the
concentration of each class and each component in the insulation
jacket, is multiplied by the specific mass of the insulation to
give the required weight of the respective class and component
therein, each such calculation being appropriately adjusted to
reflect the actual cable segment length. These products are then
summed to provide the total minimum weight of fluid mixture
required to treat the segment.
[0159] (c) A starting pressure in excess of 50 psig is assumed and
the minimum weight of fluid required from step (b) is compared to
the total weight corresponding to total volume available (i.e.,
interstitial+annular+adsorption/permeation gap) at this pressure.
The interstitial void volume can be easily calculated from the
strand conductor geometry, as described in U.S. Pat. No. 5,279,147.
The annular volume for a given cable, as a function of the
pressure, can be obtained from rigorous calculations, as described
above which provide a plot similar to FIG. 1, lower curve. The
adsorption/permeation gap volume can also be obtained from a plot
similar to FIG. 1 (upper curve for a given mix of components and
for a given cable). Alternatively, once the previously discussed
adsorption/permeation gap is experimentally determined as a
function of pressure for a given mix of components and a first
cable geometry, this data can be used to provide a good
approximation of the corresponding gap values for a second cable by
multiplying the former data by the ratio of the cross-sectional
area of the second conductor shield to that of the first cable.
[0160] (d) If there is sufficient total volume (weight) available
(which may be the case for some cables with larger and less
compacted conductors), the amount of Class S material (or a low
solubility Class Q or Class M material) is increased until the
total volume supplied equals the available total volume.
[0161] (e) If there is not sufficient total volume available at the
minimum pressure, the pressure is increased and step (c) is
iterated until at least the minimum total volume (weight) of fluid
can be accommodated.
[0162] Based on the above protocol, the candidate composition is
mixed prior to injection and the prescribed amount thereof is
injected into the interstitial void volume of the cable segment at
the appropriate pressure using one of the herein described
high-pressure connectors. Once the prescribed quantity of fluid is
delivered, the injection is terminated and the fluid confined
within the interstitial void volume at a similar residual pressure.
Thus another embodiment of the method for enhancing the cable
segment first being discussed comprises filling the interstitial
void volume of a cable segment with the amount of the dielectric
property-enhancing fluid composition required to saturate the
conductor shield and the insulation jacket of the cable segment
(W.sub.s) at a pressure P, and confining it therein at a similar
residual pressure, as previously described. In this embodiment,
when W.sub.s is greater than the weight (W.sub.i) of this
composition which can be injected into the interstitial void volume
at pressure P, the pressure is adjusted according to the above
protocol such that W.sub.s=W.sub.i. On the other hand, when W.sub.s
is less than W.sub.i, an additional weight (W) of at least one
Class S material is added to the composition before injecting the
composition such that (W+Ws)=W.sub.i.
[0163] To further clarify the above protocol, two examples of its
application are provided. These examples employ hypothetical
formulations, are provided for illustrative purposes only and do
not represent actual data. They are not to be construed as limiting
the scope of the any method discussed herein.
[0164] Example 1 illustrates the determination of the optimum
treatment for 1000 feet of concentric I/O, 100% XLPE insulation
cable. A preliminary formulation, shown in the table below, which
provides the desired reliability benefits, is selected. The
treatment fluid comprises acetophenone (a Class Q material),
vinylmethylbis(1-phenylethyleneoxy)sil- ane (VMB, a Class M
material) and S1 and S2 (two typical Class S materials). The
concentrations (weight percent=100.times.solubility in g/cm.sup.3,
where the insulation is XLPE with a density of about 1 g/cm.sup.3)
have been arbitrarily selected for optimum performance, either from
empirical observations, theoretical considerations such as
saturation levels, or both. The specific gravity of the fluid
mixture is 1.03.
1 Acetophenone VMB S1 S2 Weight % solute 1.0% 3.5% 0.5% 0.5% in
insulation jacket Weight % solute 3.0% 16.0% 1.0% 1.0% In conductor
shield
[0165] The cross-sectional areas for the insulation jacket
(A.sub.in) and the conductor shield (A.sub.cs), are each calculated
from simple geometric principles, as discussed above. These are
used to calculate the respective specific volumes (expressed in
ft.sup.3/kft) in the insulation and conductor shield, respectively,
as shown in the following table.
2 Specific volume of insulation (Vi) 2.34 =A.sub.in .multidot. 1000
ft .multidot. 1.sup.2 ft.sup.2/12.sup.2 in.sup.2 Specific volume of
conductor 0.289 =A.sub.cs .multidot. 1000 ft .multidot. 1.sup.2
ft.sup.2/12.sup.2 in.sup.2 shield (V.sub.cs)
[0166] Each specific volume is then multiplied by each selected
component concentration from the previous table. These results are
illustrated below, wherein the total calculated fluid requirement
to treat the 1000 ft segment is about 12.2 pounds and the fractions
of each of its four components are also displayed (e.g., for the
VMB fluid in the conductor shield: 0.289 (ft.sup.3/kft).times.62.4
lb/ft.sup.3.times.1.03 (density).times.0.16 (% of VMB)=2.97
lb).
3 Wt. of Aceto- Mixture phenone VMB S1 S2 Specific component mass
in 8.26 1.50 5.26 0.75 0.75 insulation Specific component mass in
3.91 0.56 2.97 0.19 0.19 conductor shield Total Component Mass
12.17 2.06 8.23 0.94 0.94
[0167] A minimum injection pressure of 300 psig is arbitrarily
chosen to provide a rapid increase in post-injection dielectric
performance and the respective amounts of fluid (expressed in
pounds for the 1000 ft segment) which can be accommodated are
calculated or obtained from a plot similar to FIG. 1, according to
the above discussed protocol. These are displayed in the table
below, wherein A.sub.i=cross-sectional area of interstices;
A.sub.a=cross-sectional annular area at 300 psig; SG=specific
gravity of fluid mix.
4 Specific mass within interstices 5.4 A.sub.i .multidot. SG
.multidot. 1000 .multidot. 62.4/12.sup.2 Specific mass within
annulus 3.00 A.sub.a .multidot. SG .multidot. 1000 .multidot.
62.4/12.sup.2 Specific mass-adsorption/permeation 2.39 From
appropriate graph Total Specific Mass Supplied 10.8
[0168] It is seen that the amount of fluid supplied at 300 psig is
only 10.8 pounds, this being 1.4 pounds (i.e., 12.2-10.8) short of
the previously determined optimum amount. The present method
teaches an increase in pressure until the optimum quantity of fluid
(i.e., 12.2 lb) can be supplied to the cable segment. For this
example, the results of the iterative calculation according to the
above described protocol wherein the pressure is increased to 359
psig are displayed in the table below, wherein A.sub.a'=annular
cross-sectional area at 359 psig.
5 Specific mass within interstices 5.4 A.sub.i' .multidot. SG
.multidot. 1000 .multidot. 62.4/12.sup.2 Specific mass within
annulus 3.61 A.sub.a .multidot. SG .multidot. 1000 .multidot.
62.4/12.sup.2 Specific mass-adsorption/permeation 3.14 From
appropriate graph Total Specific Mass Supplied 12.2
[0169] Example 2 illustrates the above protocol applied to the
optimum treatment of a 1000 ft concentric 750 kcmil, 100% XLPE
insulation, cable segment. The fluid formulation of Example 1 is
again assumed and the various calculations shown therein are made
using the corresponding dimensions of this cable's geometry.
6 Specific volume of insulation (ft.sup.3/kft) 4.84 Specific volume
of conductor shield (ft.sup.3/kft) 1.10
[0170] Again, each specific volume in the table above is multiplied
by each desired concentration component in the formulation table
(see Example 1). These results are illustrated below, wherein the
total fluid requirement to treat 1000 feet of cable is 32.0 pounds
and the respective fractions of its four components are
displayed.
7 Aceto- Mixture phenone VMB S1 S2 Specific component mass in 17.1
lb 3.11 10.89 1.55 1.55 insulation Specific component mass in 14.9
lb 2.12 11.31 0.71 0.71 conductor shield Total Component Mass 32.0
lb 5.22 22.16 2.26 2.26
[0171] A minimum injection pressure of 100 psig is chosen to
provide a rapid increase in post-injection dielectric performance.
The interstitial, annular and adsorption/permeation gap volumes are
calculated or obtained from a plot similar to FIG. 1, according to
the above described protocol, and converted to the corresponding
amount of the respective components, as shown in the following
table. The specific mass supplied at 100 psig is about 66.8 pounds,
or more than twice the minimum optimum requirement.
8 Specific mass within interstices 54.2 lb =A.sub.i .multidot. SG
.multidot. 1000 .multidot. 62.4/12.sup.2 Specific mass within
annulus 11.1 lb =A.sub.a .multidot. SG .multidot. 1000 .multidot.
62.4/12.sup.2 Specific mass-adsorption/ 1.5 lb From appropriate
graph permeation Total Specific Mass Supplied 66.8 lb
[0172] Rather than wasting the excess volume with a diluent as
taught by U.S. Pat. No. 6,162,491, the present method teaches an
increase in the supply of Class S materials which provide further
extension to the treated cable's reliable life. That increase in
the Class S materials to supply a total of the 66.8 lb of fluid, as
previous shown to be accommodated by this segment, is demonstrated
by revision of the fluid formulation, as shown in the table
below.
9 Aceto- Mixture phenone VMB S1 S2 Specific component mass in 17.1
lb 3.11 10.9 1.55 1.55 insulation Specific component mass in 14.8
lb 2.12 11.3 0.71 0.71 conductor shield Class S materials above
34.9 lb 17.45 17.45 minimum Total 66.8 lb 5.23 22.2 19.7 19.7
[0173] A further advantage of the method for enhancing the cable
segment first being discussed is the elimination of the costly and
dangerous step of evacuating a cable prior to, and during, fluid
injection. The method of the prior art is costly, primarily because
of the labor involved. An injection team must wait for complete
evacuation of the cable before injection is commenced. The prior
art method can create a potentially dangerous condition when
applied to energized cables in view Paschen's Law, which predicts a
decrease in dielectric strength of air (or other gas) at reduced
pressures. Application of a vacuum in the prior art method is
preferred and currently practiced since this facilitates a complete
fill. In the absence of a vacuum, bubbles would likely form as the
fluid flowed through termination cavities or splice cavities or
even through the tangle of interstices of the cable strands. Even
when higher pressures are utilized, the pressure is always released
once the injection is complete, and any gas bubbles which were
temporarily dissolved in the fluid at the elevated pressure will
immediately effervesce, resulting in a portion of the cable being
untreated or under treated. Further, the vacuum is desirable in the
prior art method since a typical -13 psig pressure provides a 45%
or greater driving force to accelerate the flow of fluid down the
length of cable, and indeed improves the likelihood that the fluid
will flow through the entire length of the cable and therefore
avoid a failed injection. The method for enhancing the cable
segment suffers none of these problems. First, at the preferred
pressures contemplated herein, the flow rate of the fluid is much
higher and is much more likely to scour water or contaminants with
its greater shear. Further it is believed that even if a small gas
bubble is present, it will quickly dissolve in the fluid under the
influence of the residual pressure and will not immediately
effervesce to create a new bubble. Instead, the gas will now
diffuse axially in the fluid to distribute itself at a very low
concentration, but still at a relatively high partial pressure.
Because of the high partial pressure the gas will quickly diffuse
out of the cable into the surrounding soil. Thus the method avoids
the use of such a costly and dangerous vacuum.
[0174] Another advantage of the method for enhancing the cable
segment first being discussed is that there is no need to desiccate
the strands of the cable segment. Because of the high flow and
higher sheer forces described earlier, most of the water, or other
contaminants in a cable, will be flushed from the interstices by
the injection. Even if some water is left in the strands, the
method is less sensitive to the water, because an excess of water
reactive fluid can be supplied.
[0175] Because the prior art method injects fluid through splices
which were previously installed, there is a need to test each
splice's ability to accommodate flow and pressure. Yet another
advantage of the method for enhancing the cable segment first being
discussed, when combined with the novel connectors described above,
is that there is now no need to flow test and pressure test the
strands of a medium voltage power cable. Again, because of the high
injection pressures preferably used herein it is believed that
almost all stranded cables will flow. Leak testing is obviated
since the connectors employ devices designed to accommodate the
higher pressures.
[0176] The method for selecting formulations to treat electrical
cables of the present invention by injection into a cable segment
utilizes a method of matching the needs of the cable and the cable
owner with a portfolio of materials, each of which addresses
different sets of technical, operational and economic issues. A
unique cocktail is mixed with either circuit-owner cable size
granularity, or even individual cable granularity, in order to meet
the requirements of the circuit owner. In other words performance
is optimized for each application based on a menu of end-user
choices, geometry, cable operational history, and forecasted
operational loads instead of the one-size-fits-all approach used in
the prior art. A partial list of properties and commercial elements
which may be controlled and optimized to establish a target
formulation includes the following:
[0177] Five Ps of Performance
[0178] (1) Post-failure or short-term performance (<12
months);
[0179] (2) Proactive or medium-term performance (12 months to 10
years);
[0180] (3) Preemptive or long-term performance (>10 years);
[0181] (4) Price (including fluid costs, process labor intensity,
and duration & scope of warranty);
[0182] (5) Properties (including compatibility with aluminum or
copper conductors and flammability);
[0183] Three Parameters
[0184] (6) Cable geometry;
[0185] (7) Anticipated cable temperature profile (typical) which
depends upon . . .
[0186] a. average load,
[0187] b. ground temperature at cable depth,
[0188] c. soil thermal conductivity;
[0189] (8) .DELTA.T (anticipated temperature cycling; typical)
[0190] a. maximum load,
[0191] b. minimum load,
[0192] c. soil thermal conductivity.
[0193] In the present method for selecting formulations at least
one class of fluids, more preferably two classes of fluids and even
more preferably three classes of fluids are supplied in optimum
amounts. Two or more classes are used in optimum ratios depending
on the specific geometry of the cable being treated and the
performance characteristics desired by the circuit owner. As
described above, the three classes of materials are:
[0194] Class Q--Quickly diffusing materials having a diffusion
coefficient greater than about 10-7 cm2/sec at 50.degree. C., such
as acetophenone and trimethylmethoxysilane or other high
diffusivity materials disclosed in the above cited U.S. Pat. No.
5,372,841. Such materials impart short-term performance (reactive
performance) (generally, 0 to about 12 months).
[0195] Class M--Moderately diffusing materials having a diffusion
coefficient greater than about 10.sup.-8 cm.sup.2/sec, but less
than about 10.sup.-7 cm.sup.2/sec at 50.degree. C., such as
phenylmethyldimethoxysilane and p-tolylethylmethyldimethoxysilane.
Such materials impart medium-term performance (proactive
performance) (generally about 12 to about 120 months).
[0196] Class S--Slowly diffusing materials or low solubility
materials, as discussed above, having a low solubility of about
0.0001 to about 0.02 gram/cm.sup.3 at 25.degree. C. or having a
diffusivity less than about 10.sup.-8 cm.sup.2/sec at 50.degree.
C., and having a permeability less than about 10.sup.-10 g/cm.sup.2
at 25.degree. C., each property being measured in the insulation
material, such as cyanobutylmethyldimethoxysil- ane,
cyanoethylmethyldimethoxysilane and
cyanopropylmethyldimethoxysilane. Such materials impart long-term
(preemptive) performance (generally greater than about 120
months).
[0197] A "Tailored Injection" method is illustrated in FIG. 8 with
a spiral schematic, and summarizes the impact of each of these
eight variables and also provides an overview of the optimization
methodology of the present method. The prior art single formulation
approach is an inherent compromise which attempts to balance the
eight parameters but must make trade-offs between them. The
inventors of the present method incorporate the above described
method for treating electrical cable at sustained elevated pressure
as a tool which provides a new degree of freedom in formulation
which removes many of the constraining compromises required by the
prior art approaches. The above described method for treating
electrical cable at sustained elevated pressure encompasses the
last two steps in the "Tailored Injection" spiral, namely "Adjust
pressure" and "Optimize formulation."
[0198] Disadvantages of the prior art methods which are mitigated
or eliminated with the present method for selecting formulations to
treat electrical cables include:
[0199] (1) The addition of trimethylmethoxysilane (a Class Q
compound) as suggested by U.S. Pat. No. 5,372,841 improves the
short-term performance at the expense of longer term performance
and significantly increases the vapor pressure and the flammability
of the mixture.
[0200] (2) There are no provisions for preemptive or long-term
performance. This prior art disadvantage along with the first are
discussed extensively in the above described method for treating
electrical cable at sustained elevated pressure.
[0201] (3) The reliance on a single formulation does not
accommodate substantial temperature differences (.DELTA.T) or
geometry differences between cables.
[0202] The three input parameters, namely cable geometry,
temperature, and .DELTA.T are uncontrollable parameters which
constrain the formulation choices. In the discussion which follows,
each of these three input parameters is described in detail and
strategies which may be employed to compensate for the constraints
they represent are provided.
[0203] Cable Geometry
[0204] In one sense, the cable geometry was chosen by the circuit
owner several decades prior to treatment when it was placed in the
ground. In another sense, the above described method for treating
electrical cable at sustained elevated pressure allows the
alteration of that geometry by the application of pressure. As
demonstrated above, while the starting geometry and the volume in
the interstitial spaces of the strands is unchangeable, the annulus
between the strand bundle and the conductor shield can be increased
with increasing pressure, and most unexpectedly additional fluid
can be adsorbed within the conductor shield itself. This alteration
of the cable's geometry and permeation is represented by the last
two steps in the "Tailored Injection" spiral shown in FIG. 8,
namely "Adjust pressure" and "Optimize formulation."
[0205] Anticipated Cable Temperature
[0206] Cables are well known in the art to operate over a wide
range of temperatures. Low temperatures are often the ambient
ground temperature at approximately 1 meter in depth. This
temperature typically ranges from 0.degree. C. in cryic soil
regimes common for example in Canada and Scandanaiva to 28.degree.
C. in hyperthermic soil regimes common for example in Northern
Australia, Florida, South Texas, and the low deserts of Arizona,
and when the cables are lightly loaded, the cables are very close
to uniformly at ground temperature. High temperatures for XLPE
cable may include conductor temperatures approaching their maximum
conductor design temperature of 90.degree. C. For all practical
purposes, the temperature of the conductor shield will be very
close to that of the conductor. The insulation, however, will have
a temperature profile across its radius and the typical profile
will be a function of the ambient soil temperature and the thermal
conductivity of the soil. This generalization is sufficiently
accurate for the most common case of single-phase direct-buried
cable; however, for cables in conduits or cables buried in common
trenches in close proximity with each other or duct banks, more
complex calculations, well known in the art, are utilized to
calculate temperature profiles. Permeation is the product of
diffusivity and solubility. Data available in the prior art
demonstrate that permeability changes by over an order of magnitude
over a range of approximately 40.degree. C. (see "Injection
Supersaturation," Minutes of the 104.sup.th Meeting of the IEEE,
PES, ICC, Oct. 26, 1998, Appendix A(5-30)-1, which states that "At
room temperature, [phenylmethyldimethoxysilane monomer] would take
16 months to penetrate 175 mils of insulation. At 60.degree. C.,
[phenylmethyldimethoxysilane monomer] would require about two
months to penetrate the same 175 mils."). The diffusion
coefficients for the monomer (phenylmethyldimethoxysilane, A Class
M material used in the prior art) and the oligomers
(HO(PhMeSiO).sub.xH, where x=2-5) are plotted in the "Diffusion
Coefficients f(T)" graph shown in FIG. 9. All values in FIG. 9 are
from U.S. Pat. No. 5,372,841, Table 3. It is clear that even
greater temperature fluctuations are possible and hence permeation
rates of up to two orders of magnitude must be accommodated. Unlike
the prior art one-size-fits all approach, the present method for
selecting formulations ascertains the temperature profiles which
are likely to be experienced by the cable to be treated over its
anticipated life and the formulation is modified to match the
geometry, temperature and required performance. The average
temperature profile and temperature cycling profile are considered
along with the five Ps of performance and the cable geometry. While
the diffusion coefficients of the prior art materials are generally
appropriate for average cable temperatures below 15.degree. C., the
same treatment which might last 15 years at that temperature would
be depleted after about 2 years at 60.degree. C. The present method
for selecting formulations alters the formulation in the 60.degree.
C. case to favor Class S materials which have diffusion
coefficients approximately 10 to 100 times lower.
[0207] As a non-limiting example of the forgoing, consider Example
1 of the above described method for treating electrical cable at
sustained elevated pressure where the goal was to provide the
optimum treatment for 1000 feet of concentric 1/0, 100% XLPE
insulation. Unstated in that example were the criteria of the
present method and it was assumed that the temperature (25.degree.
C.) and performance requirements were typical for such a cable. The
formulation for that case is reproduced in the table below.
10 Wt. of Aceto- Mixture phenone VMB S1 S2 Specific component mass
in 8.26 1.50 5.26 0.75 0.75 insulation Specific component mass in
3.91 0.56 2.97 0.19 0.19 conductor shield Total Component Mass
12.17 2.06 8.23 0.94 0.94
[0208] If the same cable design anticipated a typical temperature
of 50.degree. C., the present method for selecting formulations
teaches an entirely different formulation. For this example, assume
constant solubility between 25.degree. C. and 50.degree. C. and the
following diffusivities of the 4 formulation components as shown in
the first table below, wherein the thermal acceleration factor is
ratio of diffusivity at 50.degree. C. to that at 25.degree. C.
Actual diffusion coefficients and actual solubility over the
temperature range of interest can be easily measured for each
component of interest. At the higher temperature of 50.degree. C.,
the formulation in the table above would lose its short-term,
medium-term, and long-term efficacy, as shown by the "Reliable
Life@50.degree. C. (months)" column in the second table, below.
[0209] Based on accelerated life testing under the low temperature
scenario, the acetophenone is anticipated to provide reliable
performance for about 12 months. The VMB provides reliable
performance from approximately 9 months to 12 years (144
11 Thermal Diffusivity @ Diffusivity @ Acceleration Material
25.degree. C. (cm.sup.2/sec) 50.degree. C. (cm.sup.2/sec) Factor
Acetophenone 2.9 .times. 10.sup.-9 1.3 .times. 10.sup.-7 45 VMB 3.6
.times. 10.sup.-9 3.1 .times. 10.sup.-8 8.6 S1 1.6 .times.
10.sup.-10 2.6 .times. 10.sup.-9 16 S2 9.1 .times. 10.sup.-11 1.1
.times. 10.sup.-9 12
[0210] months). S1 and S2 together are anticipated to provide
reliable performance from 6 to 50 years (72-600 months). Dividing
each of these performance time periods by the thermal acceleration
factor in the above table yields new values as outlined in the
table below.
12 Reliable Reliable Life @ 25.degree. C. Life @ 50.degree. C.
Material (months) (months) Acetophenone 0-12 0-0.3 VMB 9-144 1-17
S1/S2 72-600 4.5-50
[0211] Obviously the reliability expectations at 50.degree. C. are
unacceptable in the short-term (the 20-day gap between acetophenone
depletion and VMB effectiveness) and the long-term (50 months or
4.2 years). The present method for selecting formulations (taken
together with the above described method for treating electrical
cable at sustained elevated pressure) teaches the two options
available to assure the reliability over a definable life-span:
[0212] 1. Provide more than the saturation level of components in
order to extend the reliable life within the realm in which the
individual component performs. There are four broad cases, where
cables can be provided with an excess quantity of fluid above the
saturation level without any risk of failure caused by
supersaturation or over saturation. (1) The cable is unlikely to
have prolonged or significant temperature cycling. (2) The compound
has a solubility of less than 0.02 g/cm.sup.3 at 50.degree. C. in
the insulation. (3) The compound change in solubility between the
highest typical temperature and lowest typical temperature is less
than 4. The change in solubility is defined as the solubility
(mass/unit volume) at the highest temperature to be encountered in
typical operation, S.sub.high divided by the solubility at the
lowest temperature to be encountered in typical operation to be
encountered, S.sub.low. (4). The diffusion coefficient is greater
than approximately 10.sup.-6 cm.sup.2/sec at 50.degree. C.
[0213] a. This may be accomplished by increasing the pressure to
accommodate more fluid.
[0214] b. This may be accomplished by increasing the ratio of one
component which is more desirable at the expense of a second less
critical component.
[0215] 2. Choose a different material or materials with different
solubility and diffusivity characteristics with similar or superior
restorative effects. The new material may be used to substitute for
all or a portion of the component which may cause supersaturation
or over saturation.
[0216] As is readily recognized by someone skilled in the art,
there are a variety of physical, chemical and electrical effects
know to improve cable performance. The following is a partial list
of the most important known restorative effects:
[0217] 1. Water scavenging
[0218] 2. Void filling
[0219] 3. Dielectric stress grading
[0220] 4. UV absorption
[0221] 5. Partial Discharge (PD) suppression (inception and
extinction)
[0222] Also readily appreciated by someone skilled in the art is
the portability of these effects by their inclusion as ligand
functionality in a larger treatment molecule particularly a silane,
which is itself part of cocktail of materials.] The following are
non-limiting examples of the virtually infinite number of
possibilities:
[0223] A high dielectric nitrile or cyano group can be attached to
a alkoxysilane to make an efficacious stress grading and water
scavenging fluid.
[0224] 3-methylbenzophenone is a larger analog of acetophenone and
will have lower permeability but will have similar UV absorption
effects, similar dielectric stress grading, and similar PD
suppression.
[0225] A siloxane dimer with two water reactive ligands could be
substituted for an analogous silane monomer with two water reactive
ligands to lower the solubility and the diffusion coefficient
without losing void filling, dielectric stress grading, UV
absorption, or PD suppression characteristics, and compromising
water scavenging by only 40%. (e.g.,
MeO--Si(Me)(Ph)--O--Si(Me)(Ph)--OMe is the analogous dimer of the
monomer PhMeSi(OMe).sub.2.)
[0226] As a non-limiting example, reliable performance comparable
to the 25.degree. C. results in the forgoing example could be
obtained at 50.degree. C. by making the following specific changes
shown in the table below: (1) Substitute 3-methylbenzophenone for
acetophenone in the formulation to increase the reliable life in
the short-term realm, (2) substitute a partial hydrolyzate of VMB
(designated as VMB.sup.ph) to decrease the permeation rate by a
factor of 4 to 9, and (3) substitute high temperature analogs of
both S1 and S2 (S1-ht and S2-ht) having diffusion coefficients
approximately 16 and 12 times lower, respectively. For this example
it is assumed that 3-methylbenzophenone has a permeation rate
approximately one-third that of acetophenone. There are a variety
of aromatic ketones which might be used to tailor the permeation
rate and provide suitable partial discharge extinction.
13 Mixture Methylbenzophenone VMB.sup.ph S1-ht S2-ht Specific 8.26
1.50 5.26 0.75 0.75 component mass. in insulation Specific 3.91
0.56 2.97 0.19 0.19 component mass in conductor shield Total 12.17
2.06 8.23 0.94 0.94
[0227] There is a virtually infinite number of formulation
combinations which can be devised to meet the performance
requirements. The preceding example is but a single manifestation
of those varied possibilities.
[0228] .DELTA.T
[0229] The geometry of the cable, the thermal conductivity of the
soil and the change in load (amperes) on a cable determines how
dramatic temperature changes in the cable are. The load for most
cables is seasonal and in fact highly variable throughout a given
day. Thus, for warm climate areas the maximum seasonal cable loads
are generally experienced in the summer when air-conditioner loads
are the greatest. For cold climate areas the maximum cable loads
are generally experienced in the winter when the outside
temperatures are lowest. Similarly, on a typical July day in
Austin, Tex. for example, the maximum load is reached at 4:00 PM
and sinks to its minimum load at 4:00 AM. Each locale has its own
unique load profile. Furthermore, even within a given circuit, the
minimum and maximum loads vary considerably. Consider for example
the typical 1/0 URD circuit which starts at a pole and travels
underground connecting 10 transformers in series. If each
transformers load at 4:00 PM is 15 amperes, the cable from the pole
to the first transformer (Cable 1) is carrying 10
transformers.times.15 amperes or 150 amps. The conductor of Cable 1
is likely to be in the 60-80.degree. C. range at 4:00 PM. These
types of calculation are well know in the art and are referred to
as ampacity calculations. One source for such calculations is
IEEE--IPCEA Power Cable Ampacities for Copper & Aluminum
Conductors, published jointly in 1962 by the IEEE and the IPCEA
(IEEE S-135; IPCEA P-46-426). Contrast Cable 1 to the last cable
(Cable 10) which serves only a single transformer and hence carries
only 15 amperes of current and is likely to have a conductor
temperature of approximately 25-30.degree. C. Not only do the
maximum and minimum temperature changes affect this .DELTA.T, they
also have an effect on the average anticipated temperature profile
previously described. While the prior art approach would treat all
ten of these cables identically, the present method teaches that
the formula should be varied along the length of this example
circuit. Cable 10 would not experience significant changes in
temperature (.DELTA.T) and hence there would be no constraint on
the maximum solubility or maximum concentration of any single
component. On the other hand for Cable 1, where the anticipated
.DELTA.T of the conductor is approximately 40.degree. C. and the
anticipated maximum .DELTA.T for the insulation is just less than
40.degree. C., the formulation would have to be either:
[0230] Composed entirely of components wherein the sum of the
solubilities within each class in the insulation and the shield is
less than 2% by weight at 25.degree. C., or
[0231] Those components with solubility greater than 2% would have
to be limited in the formulation such that they, and any other
sister components in the same class, could not exceed 2% by weight
in the insulation.
[0232] The insulation will generally be cooler than the conductor
temperature; however the insulation closest to the conductor will
be just slightly lower (perhaps 1.degree. C.) than the conductor
temperature.
[0233] It should be noted that in each case the anticipated
.DELTA.T is within the timeframe that the class of materials will
be present. For example, with Cable 1 above, a Class Q material
which is only going to be around for six months post-injection may
be introduced above 2% in the month of November in Austin, Tex.
since the maximum contemplated .DELTA.T for November through April
is less than 20.degree. C. These rules are generalized in the
following formula.
C.sub.max=0.05-0.0006.multidot..DELTA.T
[0234] Where,
[0235] C.sub.max is the maximum concentration as a weight fraction
(solubility and/or maximum solute) within each material class
during the time period where the material class is present at or
above the threshold concentration;
[0236] .DELTA.T is the maximum change in insulation temperature,
which is generally just slightly lower than the maximum change in
conductor temperature, and .DELTA.T is between of 0 and 75.degree.
C.
[0237] 0.05 and 0.0006 are empirical constants determined from
experiments and information available in the art for typical
cross-linked polyethylene cables. Other empirical constants could
be substituted for other cases without departing from the spirit of
the present method.
[0238] For example, suppose .DELTA.T is 50.degree. C.,
C.sub.max=0.05-0.0006.multidot..DELTA.T would equal
0.05-0.0006.multidot.50 or 0.02 weight fraction or 2%.sub.w of each
material class.
[0239] Post-Failure Performance
[0240] If a circuit owner is treating cables to extend their life
well before they have actually failed, there is little reason to
supply Class Q performance enhancing materials. This customer
treatment strategy is called proactive if there have been a few
isolated failures in cables being treated or it is preemptive if
there have been no failures. Lowering the amount of Class Q
materials allows either Price saving or an increase in the amount
of Class M and Class S materials supplied to the cable which will
extend the cable's long-term performance. The prior art approach
provides the same ratio of Class Q materials to Class M materials
without regard to the circuit owners desires. The present method
simply asks the circuit owner whether they are concerned about
short-term post injection failures or not and then adjusts the
Class Q materials as shown in the table below:
14 Customer expectation Class Q Supply There is no chance of post
injection failure Do not use Class Q materials. There is little
chance of post injection Use 50% of the maximum failure as this
cable has been failure free. allowable Class Q material(s) unless
constrained by other considerations. The cable in question has
failed more Use 75% of the maximum than 120 days prior to treatment
allowable Class Q material(s) unless constrained by other
considerations. The cable in question has failed within the Use
Class Q material(s) up the last 120 days and another failure in the
maximum allowable as short term is quite likely constrained by
other considerations.
[0241] It is possible that there are other nuances which place a
particular cable between the four categories outline above and it
is not a departure from the present method to interpolate between
the four identified cases.
[0242] Proactive Performance
[0243] If a circuit owner is treating cables preemptively well
before any cable failures are anticipated, lowering the amount of
Class Q materials and Class M materials allows either Price saving
or an increase in the amount of Class S materials supplied to the
cable which will extend the cable's long-term performance. The
prior art approach provides the same ratio of Class Q materials to
Class M materials without regard to the circuit owners desires. The
present method for selecting formulations simply asks the circuit
owner whether they are concerned about medium term reliability or
not and then adjusts the Class Q and Class M materials as shown in
the table below:
15 Customer expectation Class Q Supply The cable is likely to
provide Do not use Class Q materials. reliable performance for 2
years. The cable is likely to provide Do not use Class Q materials.
Use 50% of reliable performance the maximum allowable Class M
materials for 5 years. unless constrained by other considerations,
or decrease the average permeation of the Class M material(s) by a
factor of approximately 2. The cable is likely to provide Do not
use Class Q materials. Use 25% of reliable performance the maximum
allowable Class M materials for 10 years. unless constrained by
other considerations. Decrease the average permeation of the Class
M material(s) by a factor of approximately 4. The cable is likely
to provide Do not use Class Q materials. Do not use reliable
performance Class M materials. for 15 years.
[0244] It is possible that there are other nuances which place a
particular cable between the four categories outlined above and it
is not a departure from the present method to interpolate between
the four identified cases.
[0245] Preemptive Performance
[0246] If technology and money were not an issue, circuit owners
would desire infinite life at a very low cost. Unfortunately, both
technology and money are an issue and preemptive performance is
where the two meet. Very long life, even in excess of that provided
by new cables, is possible with the present method, particularly
when it is combined with the above described method for treating
electrical cable at sustained elevated pressure which allows a
greater amount of fluid to be supplied. While the prior art
approach provides the same ratio of Class Q materials to Class M
materials and the same total amount for fluid without regard to the
circuit owners desires, the present method for selecting
formulations simply asks the circuit owner to make the value
judgment which weighs the desired Preemptive Performance against
the Price they are willing to pay within the constraints of the
cable geometry and the available fluid technologies. This trade-off
is described as one element in the Price discussion which
follows.
[0247] Price
[0248] Obviously, the cost of each potential restorative material
can vary considerably depending on the ease of manufacture and
scale of its commercial availability. In addition to the direct
cost of the material, the cost of handling and injection can vary
depending on its physical properties. The circuit owner may choose
to compromise preemptive (or long-term) performance for price
depending upon the circuit owner's evaluation of the time value of
money. Deferred economics principles, well described in the art
(see "Recent Advances in Cable Rejuvenation Technology," IEEE/PES
Summer Meeting, 1999), are utilized to weigh the incremental cost
of extended life against the incremental extended life for a given
formulation change. For example, suppose the use of component
"omega" is know to extend the reliable life of the formulation from
30 years to 35 years and the incremental cost for using omega over
its less costly counterpart is $1.20 per foot. Is the circuit owner
best served by utilizing omega and paying the incremental $1.20?
Using the Net Present Value (NPV) analysis well known in the art,
the deferred economics of this decision are easily determined and
depend primarily on the discount factor for future cash flows and
the anticipated cost of replacement.
[0249] Properties
[0250] A wide variety of materials is available in the art which
might aid in the extension of reliable life of a circuit. Each of
these materials has other advantages, and disadvantages which must
also be considered in the formulation decision. As non-limiting
examples of this concept, it is known in the art that certain
aluminum alloys are more susceptible to corrosion by methanol than
other aluminum alloys. To the extent the circuit owner is engaged
in a process to improve the circuit reliability there is little
desire to introduce methanol to a cable which has a susceptible
alloy. In such a case the decision maker might decrease the
quantity, or even exclude, low priced and commonly used methoxy or
alkoxy silanes in favor of water reactive materials which produce
no methanol or materials which are not water reactive at all. As
another case, consider the safety aspects of including materials in
the formulation having low flash points and hence high
flammability. While these materials may be efficacious, the safety
consequences may not be allowable for certain situations, such as
duct-manhole systems where the consequences of a fire or explosion
can be fatal. The prior art uses a single active formulation for
every case. The present method for selecting formulations teaches
the inclusion of a wide variety of materials which can meet an
equally wide variety of needs and including circuit owner input to
exclude or minimize certain kinds of materials which fall outside
of allowable properties.
[0251] The present method for selecting formulations includes both
processes and business methods which together allow the formulation
to be tailored to the end-user's requirements with far fewer
compromises than the prior art approaches.
[0252] One embodiment of the present method for selecting
formulations involves injecting insulated (solid dielectrics such
as polyethylene or EPR or solid-liquid dielectrics such as
paper-oil) stranded power cables (including medium voltage, low
voltage and high voltage) to provide a tailored mixture of
treatment materials to assure reliable life for various cable
geometries and operational characteristics.
[0253] Another embodiment of the method for selecting formulations
includes considering cable geometry and the anticipated temperature
of a cable to vary the formulation of at least one injection
compound.
[0254] The method for selecting formulations may be used where one
or more of the following are considered to provide an optimum
formulation:
[0255] a. Post-failure or short-term performance (<12
months);
[0256] b. Proactive or medium-term performance (12 months to 10
years);
[0257] c. Preemptive or long-term performance (>10 years);
[0258] d. Price (including fluid costs, process labor intensity,
and duration & scope of warranty);
[0259] e. Properties (including compatibility with aluminum or
copper conductors and flammability).
[0260] The method for selecting formulations may be employed where
the anticipated temperature includes both anticipated typical
temperature and the anticipated typical temperature cycles.
[0261] The method for selecting formulations may be practiced where
the variable formulation includes injection compounds from at least
two different classes.
[0262] The method may also be practiced where the variable
formulation includes injection compounds from at least three
different classes.
[0263] Combinations of various aspects of the method for selecting
formulations may be utilized but for brevity are not all set forth
herein.
* * * * *